Plug Debugger wrap exception text (#1241)

Sometimes exceptions print out with really long lines which makes it
difficult to read the exceptions on the error page.

lib/plug/templates/debugger.html.eex

@@ -146,8 +146,13 @@
 
     .exception-info > code {
         line-height: 1.5;
+        font-size: <%= :math.pow(1.3, -1) %>em;
     }
 
+    .exception-details-text {
+        white-space: pre-wrap;
+     }
+
     /*
      * Code explorer
      */
@@ -681,7 +686,7 @@
                 <small>at <%= h method(@conn) %></small>
                 <small class="path"><%= h @conn.request_path %></small>
             </h5>
-            <code><pre><%= h @message %></pre></code>
+            <code><pre class="exception-details-text"><%= h @message %></pre></code>
         </header>
 
         <%= for %{label: label, encoded_handler: encoded_handler} <- @actions do %>