Fix typos in RouterGroup method docs (gin-gonic#3302)

There were a number of spots referring to a variable named "handle" that should be "handlers".

routergroup.go

@@ -106,37 +106,37 @@ func (group *RouterGroup) Handle(httpMethod, relativePath string, handlers ...Ha
 	return group.handle(httpMethod, relativePath, handlers)
 }
 
-// POST is a shortcut for router.Handle("POST", path, handle).
+// POST is a shortcut for router.Handle("POST", path, handlers).
 func (group *RouterGroup) POST(relativePath string, handlers ...HandlerFunc) IRoutes {
 	return group.handle(http.MethodPost, relativePath, handlers)
 }
 
-// GET is a shortcut for router.Handle("GET", path, handle).
+// GET is a shortcut for router.Handle("GET", path, handlers).
 func (group *RouterGroup) GET(relativePath string, handlers ...HandlerFunc) IRoutes {
 	return group.handle(http.MethodGet, relativePath, handlers)
 }
 
-// DELETE is a shortcut for router.Handle("DELETE", path, handle).
+// DELETE is a shortcut for router.Handle("DELETE", path, handlers).
 func (group *RouterGroup) DELETE(relativePath string, handlers ...HandlerFunc) IRoutes {
 	return group.handle(http.MethodDelete, relativePath, handlers)
 }
 
-// PATCH is a shortcut for router.Handle("PATCH", path, handle).
+// PATCH is a shortcut for router.Handle("PATCH", path, handlers).
 func (group *RouterGroup) PATCH(relativePath string, handlers ...HandlerFunc) IRoutes {
 	return group.handle(http.MethodPatch, relativePath, handlers)
 }
 
-// PUT is a shortcut for router.Handle("PUT", path, handle).
+// PUT is a shortcut for router.Handle("PUT", path, handlers).
 func (group *RouterGroup) PUT(relativePath string, handlers ...HandlerFunc) IRoutes {
 	return group.handle(http.MethodPut, relativePath, handlers)
 }
 
-// OPTIONS is a shortcut for router.Handle("OPTIONS", path, handle).
+// OPTIONS is a shortcut for router.Handle("OPTIONS", path, handlers).
 func (group *RouterGroup) OPTIONS(relativePath string, handlers ...HandlerFunc) IRoutes {
 	return group.handle(http.MethodOptions, relativePath, handlers)
 }
 
-// HEAD is a shortcut for router.Handle("HEAD", path, handle).
+// HEAD is a shortcut for router.Handle("HEAD", path, handlers).
 func (group *RouterGroup) HEAD(relativePath string, handlers ...HandlerFunc) IRoutes {
 	return group.handle(http.MethodHead, relativePath, handlers)
 }