Fix a typo in GN documentation

tools/gn/docs/reference.md

 # GN Reference
 
 *This page is automatically generated from* `gn help --markdown all`.
 
 ## **\--args**: Specifies build arguments overrides.
 
 ```
   See "gn help buildargs" for an overview of how build arguments work.
 
   Most operations take a build directory. The build arguments are taken from
@@ skipping 6566 matching lines @@
       source file is in a different directory than the BUILD.gn file.
         "//foo/bar/baz.txt" => "gen/foo/bar"
 
   {{source_out_dir}}
       The object file directory (*) corresponding to the source file's path,
       relative to the build directory. this us be different than the target's
       out directory if the source file is in a different directory than the
       build.gn file.
         "//foo/bar/baz.txt" => "obj/foo/bar"
 
-  {{source_target_relative}}\n"
+  {{source_target_relative}}
       The path to the source file relative to the target's directory. This will
       generally be used for replicating the source directory layout in the
       output directory. This can only be used in actions and it is an error to
       use in process_file_template where there is no "target".
         "//foo/bar/baz.txt" => "baz.txt"
 
 ```
 
 ### **(*) Note on directories**
 
@@ skipping 54 matching lines @@
 **  \--root**: Explicitly specify source root.
 **  \--runtime-deps-list-file**: Save runtime dependencies for targets in file.
 **  \--script-executable**: Set the executable used to execute scripts.
 **  \--threads**: Specify number of worker threads.
 **  \--time**: Outputs a summary of how long everything took.
 **  \--tracelog**: Writes a Chrome-compatible trace log to the given file.
 **  -v**: Verbose logging.
 **  \--version**: Prints the GN version number and exits.
 
 ```