Fix an obsolete comment.

Change-Id: I89e97b070a3cc5c413d8bc44504ff2235942039d
diff --git a/src/runtime.cc b/src/runtime.cc
index bedeb27..f434fed 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -809,7 +809,7 @@
   if (sigaddset(&sigset, SIGQUIT) == -1) {
     PLOG(ERROR) << "sigaddset SIGQUIT failed";
   }
-  // SIGUSR1 is used to initiate a heap dump.
+  // SIGUSR1 is used to initiate a GC.
   if (sigaddset(&sigset, SIGUSR1) == -1) {
     PLOG(ERROR) << "sigaddset SIGUSR1 failed";
   }