Try using sudo: false (learned from commercialhaskell/stack#458)

.travis.yml

@@ -1,12 +1,16 @@
-env:
- - CABALVER=1.22 GHCVER=7.10.1
+sudo: false
+
+addons:
+  apt:
+    sources:
+    - hvr-ghc
+    packages:
+    - ghc-7.10.1
+    - cabal-install-1.22
 
 # Note: the distinction between `before_install` and `install` is not important.
 before_install:
- - travis_retry sudo add-apt-repository -y ppa:hvr/ghc
- - travis_retry sudo apt-get update
- - travis_retry sudo apt-get install cabal-install-$CABALVER ghc-$GHCVER # see note about happy/alex
- - export PATH=/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$PATH
+ - export PATH=/opt/ghc/7.10.1/bin:/opt/cabal/1.22/bin:$PATH
 
 install:
  - cabal --version