Fix doc links in str::escape_{debug, default, unicode}

[awaitlink]

Links to char::escape_{debug, default, unicode} in str::escape_{debug, default, unicode} documentation start with ../std/ but should start with ../../std/ to not 404.

[rust-highfive]

r? @KodrAus

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[ollie27]

This will fix the links on https://doc.rust-lang.org/nightly/std/string/struct.String.html#method.escape_debug but break the links on https://doc.rust-lang.org/nightly/std/primitive.str.html#method.escape_debug. This is #32129 for which there is no complete solution yet.

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:01c7d174:start=1555246532610861516,finish=1555246533383886425,duration=773024909
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
travis_time:start:test_assembly
Check compiletest suite=assembly mode=assembly (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:19:27] 
[01:19:27] running 9 tests
[01:19:27] iiiiiiiii
[01:19:27] 
[01:19:27]  finished in 0.189
[01:19:27] travis_fold:end:test_assembly

---
travis_time:start:test_debuginfo
Check compiletest suite=debuginfo mode=debuginfo-both (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:19:46] 
[01:19:46] running 121 tests
[01:20:16] .iiiii...i.....i..i...i..i.i.i..i.ii...i.....i..i....i..........iiii..........i...ii...i.......ii.i. 100/121
[01:20:22] i.i......iii.i.....ii
[01:20:22] 
[01:20:22]  finished in 35.779
[01:20:22] travis_fold:end:test_debuginfo

---
[01:50:12] travis_fold:end:stage0-linkchecker

[01:50:12] travis_time:end:stage0-linkchecker:start=1555253155310759135,finish=1555253157582462053,duration=2271702918

[01:50:15] std/primitive.str.html:1142: broken link - /checkout/obj/build/x86_64-unknown-linux-gnu/std/primitive.char.html
[01:50:15] std/primitive.str.html:1165: broken link - /checkout/obj/build/x86_64-unknown-linux-gnu/std/primitive.char.html
[01:50:15] std/primitive.str.html:1186: broken link - /checkout/obj/build/x86_64-unknown-linux-gnu/std/primitive.char.html
[01:50:24] thread 'main' panicked at 'found some broken links', src/tools/linkchecker/main.rs:41:9
[01:50:24] 
[01:50:24] 
[01:50:24] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/linkchecker" "/checkout/obj/build/x86_64-unknown-linux-gnu/doc"
[01:50:24] expected success, got: exit code: 101
[01:50:24] expected success, got: exit code: 101
[01:50:24] 
[01:50:24] 
[01:50:24] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:50:24] Build completed unsuccessfully in 0:44:20
[01:50:24] Makefile:48: recipe for target 'check' failed
[01:50:24] make: *** [check] Error 1
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0d138dc7
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Sun Apr 14 14:46:10 UTC 2019
---
travis_time:end:17bc1c18:start=1555253173151116224,finish=1555253173231373112,duration=80256888
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:1907094f
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:070eb53c
$ dmesg | grep -i kill

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