Add syntax highlighting to files

app/assets/javascripts/merge_conflicts/components/diff_file_editor.js.es6

@@ -55,6 +55,7 @@
             this.fileLoaded = true;
             this.editor = ace.edit(content);
             this.editor.$blockScrolling = Infinity; // Turn off annoying warning
+            this.editor.getSession().setMode(`ace/mode/${file.blob_ace_mode}`);
             this.editor.on('change', () => {
               this.saveDiffResolution();
             });