Update the dlmalloc submodule

alexcrichton · alexcrichton · commit bb0df9602edd · 2018-02-08T20:45:45.000-08:00
A bug was recently fixed in dlmalloc which meant that released memory to the
system accidentally wasn't getting reused, causing programs to be far slower
than they should be!
diff --git a/src/dlmalloc b/src/dlmalloc
@@ -1 +1 @@
-Subproject commit d3812c3accaee7ad23068ed4fc089cc05c7a538f
+Subproject commit 8c3141db4f8ef2fb0154740c87d6970ec7752d74
