Remove Get, reuse counter value returned by incr operation

[ankitd009]

Avoid making an extra Get call to read counter's value, use the incremented value returned by INCR operation.

Testing Strategy: existing tests for rate limit should pass.

c.Send("MULTI")
c.Send("INCR", "foo")
c.Send("EXPIRE", "foo", 300)
r, err := c.Do("EXEC")
// prints [1, 1]
// r[0] result of incr operation
// r[1 ] result of expire, 1 if the timeout was set, 0 if key does not exist.
fmt.Println(r) 

Redis-Expire Doc
Redigo-Pipeline Doc