Added asymptote package requirement to .travis.yml

.travis.yml

@@ -33,6 +33,15 @@ matrix:
 #   - env: RACKET_VERSION=HEAD
   fast_finish: true
 
+branches:
+  only:
+    - master
+
+addons:
+  apt:
+    packages:
+    - asymptote
+
 before_install:
 - git clone https://github.com/greghendershott/travis-racket.git ~/travis-racket
 - cat ~/travis-racket/install-racket.sh | bash # pipe to bash not sh!