travis: Build mpy-cross as part of the Travis process.

dpgeorge · dpgeorge · commit e4d6a10dc91f · 2016-09-05T17:33:56.000+10:00
It's built first in case any ports need to use it.
diff --git a/.travis.yml b/.travis.yml
@@ -23,6 +23,7 @@ before_script:
   - python3 --version
 
 script:
+  - make -C mpy-cross
   - make -C minimal test
   - make -C unix deplibs
   - make -C unix
