Issue 813. Made watch interval configurable through global setting in Taskfile and through CLI arg.

Separated Taskfile param and Arg flag

task.go

@@ -41,6 +41,7 @@ type Executor struct {
 	Parallel    bool
 	Color       bool
 	Concurrency int
+	Interval    string
 
 	Stdin  io.Reader
 	Stdout io.Writer