run-tests: assign value to ESCAPEMAP - dict.update do not return self

a36cc85a5b7b did more than what the description said and introduced a bug.

tests/run-tests.py

@@ -686,8 +686,8 b' class TTest(Test):'
     NEEDESCAPE = re.compile(r'[\x00-\x08\x0b-\x1f\x7f-\xff]').search
 
     ESCAPESUB = re.compile(r'[\x00-\x08\x0b-\x1f\\\x7f-\xff]').sub
-    ESCAPEMAP = dict((chr(i), r'\x%02x' % i) for i in range(256)).update(
-                     {'\\': '\\\\', '\r': r'\r'})
+    ESCAPEMAP = dict((chr(i), r'\x%02x' % i) for i in range(256))
+    ESCAPEMAP.update({'\\': '\\\\', '\r': r'\r'})
 
     @property
     def refpath(self):