Made some changes based on review comments

Author: maknahar

mux.go

@@ -14,7 +14,7 @@ import (
 )
 
 var (
-	ErrMethodMismatch = errors.New("Method is Not Allowed")
+	ErrMethodMismatch = errors.New("method is not allowed")
 )
 
 // NewRouter returns a new router instance.

mux_test.go

@@ -1872,7 +1872,7 @@ func newRequest(method, url string) *http.Request {
 	return req
 }
 
-func TestNoMatchMethodErrors(t *testing.T) {
+func TestNoMatchMethodErrorHandler(t *testing.T) {
 	func1 := func(w http.ResponseWriter, r *http.Request) {}
 
 	r := NewRouter()

old_test.go

@@ -121,7 +121,7 @@ func TestRouteMatchers(t *testing.T) {
 		var routeMatch RouteMatch
 		matched := router.Match(request, &routeMatch)
 		if matched != shouldMatch {
-			t.Errorf("Match Expectation: %v\nGot: %v\nRequest: %v %v", shouldMatch, matched, request.Method, url)
+			t.Errorf("Expected: %v\nGot: %v\nRequest: %v %v", shouldMatch, matched, request.Method, url)
 		}
 
 		if matched {