patch 8.1.1828: not strict enough checking syntax of method invocation

Problem:    Not strict enough checking syntax of method invocation.
Solution:   Check there is no white space inside ->method(.
diff --git a/src/testdir/test_method.vim b/src/testdir/test_method.vim
index 02c69f2..7780f08 100644
--- a/src/testdir/test_method.vim
+++ b/src/testdir/test_method.vim
@@ -112,3 +112,13 @@
 
   delfunc Concat
 endfunc
+
+func Test_method_syntax()
+  eval [1, 2, 3]  ->sort( )
+  eval [1, 2, 3]  
+	\ ->sort(
+	\ )
+  call assert_fails('eval [1, 2, 3]-> sort()', 'E260:')
+  call assert_fails('eval [1, 2, 3]->sort ()', 'E274:')
+  call assert_fails('eval [1, 2, 3]-> sort ()', 'E260:')
+endfunc