Added mysql v5.5.30 to formula.

- Thanks Obama(Oracle)! For dropping mysql versions less than 5.5.30.
- The most recent version of mysql 5.5.x that homebrew supports is 5.5.29. The oldest version that Oracle hosts is 5.5.30. 
- The newest versions of mysql 5.5.x, namely, 5.5.31 and 5.5.32 do not build. Hence, 5.5.30.