Revert "Bump diff-lcs ~> 1.2.0"
Revert "Bump diff-lcs ~> 1.2.0"

This reverts commit 41130fe6dc91be4a35cf7f4122ac1b28f53c5037.

* Rspec is not compatible with diff-lcs ~> 1.2.0

backus/mutest,tjchambers/mutant,backus/mutant,kbrock/mutant,nepalez/mutant,backus/mutest