Fix a trivial typo in grokdump.py

Change-Id: I5977c58d7d39f5f13352234f0d016c47ce9be133
Reviewed-on: https://chromium-review.googlesource.com/1143465Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Tobias Sargeant <tobiasjs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54562}

tools/grokdump.py

@@ -761,7 +761,7 @@ class MinidumpReader(object):
 
   def IsValidExceptionStackAddress(self, address):
     if not self.IsValidAddress(address): return False
-    return self.isExceptionStackAddress(address)
+    return self.IsExceptionStackAddress(address)
 
   def IsModuleAddress(self, address):
     return self.GetModuleForAddress(address) != None