Fix kill method (GentleKillingExecutor)
Use 0.1.5 version of mirakuru

Use os.killpg to terminate process (GentleKillingExecutor)
Update requires (mirakuru to 0.2)

Update requires (mirakuru to 0.2)
Merge pull request #72 from ClearcodeHQ/fix-gentle-executor

Fix kill method (GentleKillingExecutor)