Fix missing space in heap_profile.

Change-Id: I1e5ce0f1593126f4c52315c12576dfacc7acc805

tools/heap_profile

diff --git a/tools/heap_profile b/tools/heap_profile
index eaac620..8388755 100755
--- a/tools/heap_profile
+++ b/tools/heap_profile
@@ -219,7 +219,7 @@
       action="store_true")
   parser.add_argument(
       "--dump-at-max",
-      help="Dump the maximum memory usage"
+      help="Dump the maximum memory usage "
       "rather than at the time of the dump.",
       action="store_true")
   parser.add_argument(