docs($browser-support): #1180 - Update Safari 5.1 chunking support

Only certain builds of Safari 5.1 have chunking support:

- https://developer.mozilla.org/en-US/docs/Web/API/Blob#Browser_compatibility
- http://trac.webkit.org/changeset/83873
- https://github.com/blueimp/jQuery-File-Upload/issues/2014#issuecomment-12503731

[skip ci]

Closes #1180