Treat minified files as binary for git

This prevents e.g. `git log -p` from showing the content changes in
these files by default, which is what we want because line-oriented
diffs of these files are meaningless.

.gitattributes

@@ -14,6 +14,8 @@
 *.jpg -diff binary image
 *.jpeg -diff binary image
 *.pbm -diff binary image
+*.min.js -diff binary minified
+*.min.css -diff binary minified
 /clients/flex* dfsg-nonfree
 /debian* debian-ignore
 /freeswitch.xcodeproj debian-ignore