update location to a working copy of gulp-requirejs

For some reason, http://github.com/RobinThrift/gulp-requirejs is gone (404), but if you use http://github.com/bornkiller/gulp-requirejs
then it works.

This fixes issue #596"
More permissive code block labels. Fixes #600
Updated flowchart lib
Updated fontello icons. Fixes #592
Prepare release
Merge branch 'master' of github.com:benweet/stackedit
Merge branch 'master' into gulp_requirejs_disappeared
Merge branch 'master' into plugins