graphviz: fix dotty label bug

This patch is already in upstream, posterior to graphviz-2.34.0.

Closes Homebrew/homebrew#25187

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/graphviz.rb

@@ -37,9 +37,15 @@ class Graphviz < Formula
   end
 
   def patches
-    {:p0 =>
+    p = {:p0 =>
       "https://trac.macports.org/export/103168/trunk/dports/graphics/graphviz/files/patch-project.pbxproj.diff",
      }
+
+     # The following patch is already upstream and can be removed in the next release.
+     if build.stable?
+       p[:p1] = "https://gist.github.com/mvertes/7929246/raw/2093e77bbed7ca0f4092f478cae870e021cbe5af/graphviz-2.34.0-dotty-patch"
+     end
+     return p
   end
 
   def install