Fix tested Ruby versions in README

References #1100

Author: hisas

README.md

@@ -42,17 +42,15 @@ me a nice email :)
 Compatibility
 -------------
 
-Every Mail commit is tested by Travis on the [following platforms](https://github.com/mikel/mail/blob/master/.travis.yml)
-
-* ruby-1.8.7 [ i686 ]
-* ruby-1.9.2 [ x86_64 ]
-* ruby-1.9.3 [ x86_64 ]
-* ruby-2.0.0 [ x86_64 ]
-* ruby-2.1.2 [ x86_64 ]
-* ruby-head [ x86_64 ]
-* jruby [ x86_64 ]
-* jruby-head [ x86_64 ]
-* rbx-2 [ x86_64 ]
+Mail supports Ruby 1.8.7+, including JRuby and Rubinius.
+
+Every Mail commit is tested by Travis on [all supported Ruby versions](https://github.com/mikel/mail/blob/master/.travis.yml).
+
+Testing a specific version of mime-types (needed for Ruby 1.8.7, for example) can be done manually with:
+
+```sh
+BUNDLE_GEMFILE=gemfiles/mime_types_1.16.gemfile bundle && rake
+```
 
 Discussion
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