Don't pin dev tools versions.

aaugustin · aaugustin · commit 1ad8c54df122 · 2013-11-01T18:46:50.000+01:00
We'll usually want the most recent version of these tools. They're only
used in development anyway.
diff --git a/requirements_dev.txt b/requirements_dev.txt
@@ -18,6 +18,6 @@ Sphinx
 
 # Other tools
 
-transifex-client==0.9.1
-wheel==0.22.0
-yuicompressor==2.4.8
+transifex-client
+wheel
+yuicompressor
