docs: Fix a few typos

[timgates42]

There are small typos in:

• grappelli/static/grappelli/tinymce/jscripts/tiny_mce/plugins/autosave/editor_plugin_src.js
• grappelli/static/grappelli/tinymce/jscripts/tiny_mce/plugins/media/editor_plugin_src.js
• grappelli/static/grappelli/tinymce/jscripts/tiny_mce/plugins/media_orig/editor_plugin_src.js

Fixes:

• Should read context rather than contect.
• Should read preferable rather than preferrable.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md