Merge branch 'gfm-commit' into 'master'

commit hashes are monospaced

Use a monospaced font for GFM commit and commit range references

See merge request !914

app/assets/stylesheets/generic/gfm.scss

@@ -19,3 +19,7 @@
     height: 14em;
   }
 }
+
+.gfm-commit, .gfm-commit_range {
+  font-family: $monospace_font;
+}