fetch-mock: method option is optional

Actually, it should be never but to keep compatibility,
we decided to make this method option optional

https://github.com/DefinitelyTyped/DefinitelyTyped/pull/29264#discussion_r221364845

types/fetch-mock/fetch-mock-tests.ts

@@ -62,6 +62,7 @@ fetchMock.patchOnce("http://test.com", 200);
 
 fetchMock.get("http://test.com", 200, {method: "GET"});
 fetchMock.get("http://test.com", 200, {method: "GET", overwriteRoutes: true});
+fetchMock.get("http://test.com", 200, {overwriteRoutes: true});
 fetchMock.post("http://test.com", 200, {method: "POST"});
 fetchMock.put("http://test.com", 200, {method: "PUT"});
 fetchMock.delete("http://test.com", 200, {method: "DELETE"});

types/fetch-mock/index.d.ts

@@ -6,6 +6,7 @@
 //                 Chris Sinclair <https://github.com/chrissinclair>
 //                 Matt Tennison <https://github.com/matttennison>
 //                 Quentin Bouygues <https://github.com/quentinbouygues>
+//                 Fumiaki Matsushima <https://github.com/mtsmfm>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.2
 
@@ -165,23 +166,23 @@ declare namespace fetchMock {
     }
 
     interface MockOptionsMethodGet extends MockOptions {
-    method: 'GET';
+        method?: 'GET';
     }
 
     interface MockOptionsMethodPost extends MockOptions {
-    method: 'POST';
+        method?: 'POST';
     }
 
     interface MockOptionsMethodPut extends MockOptions {
-    method: 'PUT';
+        method?: 'PUT';
     }
 
     interface MockOptionsMethodDelete extends MockOptions {
-    method: 'DELETE';
+        method?: 'DELETE';
     }
 
     interface MockOptionsMethodHead extends MockOptions {
-    method: 'HEAD';
+        method?: 'HEAD';
     }
 
     interface FetchMockStatic {