Fix test for nightly Python (3.9)

Author: PetterS

pyflakes/test/test_api.py

@@ -447,19 +447,26 @@ def evaluate(source):
             self.fail()
 
         with self.makeTempFile(source) as sourcePath:
+            message = 'invalid syntax'
+            column = 11
+            whitespace_before_caret = 10
             if PYPY:
                 message = 'end of file (EOF) while scanning triple-quoted string literal'
-            else:
-                message = 'invalid syntax'
+            elif sys.version_info >= (3, 9):
+                message = 'invalid string prefix'
+                column = 52
+                whitespace_before_caret = 15
+            elif sys.version_info >= (3, 8):
+                column = 8
+                whitespace_before_caret = 7
 
-            column = 8 if sys.version_info >= (3, 8) else 11
             self.assertHasErrors(
                 sourcePath,
                 ["""\
 %s:8:%d: %s
     '''quux'''
 %s^
-""" % (sourcePath, column, message, ' ' * (column - 1))])
+""" % (sourcePath, column, message, ' ' * whitespace_before_caret)])
 
     def test_eofSyntaxError(self):
         """