Revert "README: Add Coveralls badge"
Revert "README: Add Coveralls badge"

This reverts commit 5e148d6b204f54001d125bf59623befc07e6eaaa.

zuazo/mysql_tuning-cookbook,onddo/mysql_tuning-cookbook,zuazo/mysql_tuning-cookbook,onddo/mysql_tuning-cookbook,onddo/mysql_tuning-cookbook,zuazo/mysql_tuning-cookbook