Update CodeMirror to 5.15.2

Interesting changes in the core library that might affect Gerrit
include:
  - Fix issue where the editor would complain about overlapping
    collapsed ranges when there weren't any.
  - Optimize document tree building when loading or pasting huge chunks
    of content.

No new language mode was added. Some improvements were done on several
existing language modes:
  - markdown mode: Fix several issues in matching link targets.
  - clike mode: Improve indentation of C++ template declarations.
  - javascript mode: Support async / await and improve support for
    TypeScript type syntax.

Change-Id: If40cb074527e7dcc73d1630c89baa5fe713b44bc

lib/codemirror/BUCK

@@ -1,14 +1,14 @@
 include_defs('//lib/maven.defs')
 include_defs('//lib/codemirror/cm.defs')
 
-VERSION = '5.14.2'
+VERSION = '5.15.2'
 TOP = 'META-INF/resources/webjars/codemirror/%s' % VERSION
 TOP_MINIFIED = 'META-INF/resources/webjars/codemirror-minified/%s' % VERSION
 
 maven_jar(
   name = 'codemirror-minified',
   id = 'org.webjars.npm:codemirror-minified:' + VERSION,
-  sha1 = 'c69056d2a0e07432326e67ea8fe2abb91a065030',
+  sha1 = '222152d6c4f9da6e812378499894e6f86688ac2a',
   attach_source = False,
   license = 'codemirror-minified',
   visibility = [],
@@ -17,7 +17,7 @@ maven_jar(
 maven_jar(
   name = 'codemirror-original',
   id = 'org.webjars.npm:codemirror:' + VERSION,
-  sha1 = '1ed9697531be85c85edb70fcdf58f10045563f7b',
+  sha1 = '2f0c3e94bb133df1f07800ff0e361da8ac791442',
   attach_source = False,
   license = 'codemirror-original',
   visibility = [],