Travis: don't build with lts-3.

It doesn't have recent enough dependencies.

.travis.yml

@@ -49,10 +49,6 @@ matrix:
 
   # The Stack builds. We can pass in arbitrary Stack arguments via the ARGS
   # variable, such as using --stack-yaml to point to a different file.
-  - env: BUILD=stack ARGS="--resolver lts-3"
-    compiler: ": #stack 7.10.2"
-    addons: {apt: {packages: [ghc-7.10.2], sources: [hvr-ghc]}}
-
   - env: BUILD=stack ARGS="--resolver lts-5"
     compiler: ": #stack 7.10.3"
     addons: {apt: {packages: [ghc-7.10.3], sources: [hvr-ghc]}}