Add travis support via .travis.yml and bash bootstrap script

.travis.yml

+language: c
+
+env:
+  - FISH_PPA=nightly-master
+
+before_install:
+  - script/bootstrap.sh
+
+script: fish ./spec/spec.fish

script/bootstrap.sh

+#!/usr/bin/env bash
+ppa=ppa:fish-shell/${FISH_PPA:-nightly-master}
+sudo add-apt-repository -y $ppa
+sudo apt-get update
+sudo apt-get -y install fish
+curl -L https://github.com/bpinto/oh-my-fish/raw/master/tools/install.fish | FORK=bucaran fish