Fixes regex for timestamps to when behind GMT

Currently, a timezone that ends in say '+0200' will get stripped, but a
timezone _behind_ GMT will not (so a timezone in the United States of
say, '-0400' will **not** get stripped.

This regex change fixes that.

src/diff-parser.js

@@ -435,7 +435,7 @@
       // Cleanup timestamps generated by the unified diff (diff command) as specified in
       // https://www.gnu.org/software/diffutils/manual/html_node/Detailed-Unified.html
       // Ie: 2016-10-25 11:37:14.000000000 +0200
-      filename = filename.replace(/\s+\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}(?:\.\d+)? \+\d{4}.*$/, '');
+      filename = filename.replace(/\s+\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}(?:\.\d+)? [-+]\d{4}.*$/, '');
     }
 
     return filename;

test/diff-parser-tests.js

@@ -432,8 +432,6 @@ describe('DiffParser', function() {
         });
         assert.deepEqual(linesContent, ['-test', '+test1r', '+test2r']);
       });
-
-      
     });
 
     it('should parse unified non git diff', function() {