add travis

.travis.yml

@@ -0,0 +1,15 @@
+sudo: false
+language: c
+addons:
+  apt:
+    packages:
+    - libgmp-dev
+before_install:
+- mkdir -p ~/.local/bin
+- export PATH=$HOME/.local/bin:$PATH
+- travis_retry curl -L https://www.stackage.org/stack/linux-x86_64 | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
+script:
+- stack --install-ghc test
+cache:
+  directories:
+  - $HOME/.stack