Update travis to always use the latest release

Author: garyb

.travis.yml

@@ -1,18 +1,15 @@
 language: node_js
 node_js:
-  - "0.10"
+  - 0.10
 env:
-  - PATH=$HOME/bin:$PATH purescript_datadir=$HOME/.local/share/purescript
-before_install:
-  - mkdir -p $HOME/bin
-  - mkdir -p $HOME/.local/share/purescript/prelude
+  - PATH=$HOME/purescript:$PATH
 install:
-  - wget https://github.com/purescript/purescript/releases/download/v0.5.7.1/linux64.tar.gz
-  - tar zxvf linux64.tar.gz
-  - cp purescript/{docgen,psc,psci,psc-make} $HOME/bin
-  - cp purescript/prelude.purs $purescript_datadir/prelude/prelude.purs
-  - "npm install bower grunt-cli -g"
-  - "npm install"
-  - "bower install"
+  - TAG=$(wget -q -O - https://github.com/purescript/purescript/releases/latest --server-response --max-redirect 0 2>&1 | sed -n -e 's/.*Location:.*tag\///p')
+  - wget -O $HOME/purescript.tar.gz https://github.com/purescript/purescript/releases/download/$TAG/linux64.tar.gz
+  - tar -xvf $HOME/purescript.tar.gz -C $HOME/
+  - chmod a+x $HOME/purescript
+  - npm install bower grunt-cli -g
+  - npm install
+  - bower install
 script:
-  - "grunt test"
+  - grunt test