Merge pull request #145 from snar/freebsd-uses-gmake

When compiling on FreeBSD, use gmake instead of make.

rebar.config

@@ -11,6 +11,7 @@
 
 {pre_hooks,
  [{compile, "make -C $REBAR_DEPS_DIR/merl all"},
+  {"freebsd", compile, "gmake -C $REBAR_DEPS_DIR/merl all"},
   {eunit,
    "erlc -I include/erlydtl_preparser.hrl -o test"
    " test/erlydtl_extension_testparser.yrl"}