Run force-unlock with -no-color flag (#270)

diff --git a/tfexec/force_unlock.go b/tfexec/force_unlock.go
index c8dddff..e501baf 100644
--- a/tfexec/force_unlock.go
+++ b/tfexec/force_unlock.go
@@ -36,7 +36,7 @@
 	for _, o := range opts {
 		o.configureForceUnlock(&c)
 	}
-	args := []string{"force-unlock", "-force"}
+	args := []string{"force-unlock", "-no-color", "-force"}
 
 	// positional arguments
 	args = append(args, lockID)