gist-logs: close temp file before passing to curl (#418)

Ensures that the data gets written to disk so curl can see it, avoiding
intermittent JSON parsing errors in gist creation.

Library/Homebrew/utils/github.rb

@@ -140,6 +140,7 @@ module GitHub
     begin
       if data
         data_tmpfile.write data
+        data_tmpfile.close
         args += ["--data", "@#{data_tmpfile.path}"]
       end