cindex-dump.py: fix the --show-ids description string

It looks like this was botched back in r94936.

llvm-svn: 207947
diff --git a/clang/bindings/python/examples/cindex/cindex-dump.py b/clang/bindings/python/examples/cindex/cindex-dump.py
index 99d0390..5556ad1 100644
--- a/clang/bindings/python/examples/cindex/cindex-dump.py
+++ b/clang/bindings/python/examples/cindex/cindex-dump.py
@@ -63,7 +63,7 @@
 
     parser = OptionParser("usage: %prog [options] {filename} [clang-args*]")
     parser.add_option("", "--show-ids", dest="showIDs",
-                      help="Don't compute cursor IDs (very slow)",
+                      help="Compute cursor IDs (very slow)",
                       action="store_true", default=False)
     parser.add_option("", "--max-depth", dest="maxDepth",
                       help="Limit cursor expansion to depth N",