Travis: rename vim72 to vim74 (#723)

.travis.yml

@@ -7,7 +7,7 @@ env:
     - PATH=$DEPS/bin:$PATH
 matrix:
   include:
-    - env: ENV=vim72
+    - env: ENV=vim74
       rvm: 1.8.7
       addons: { apt: { packages: [vim-nox] } }
     - env: ENV=python
@@ -26,7 +26,7 @@ install: |
   git config --global user.email "you@example.com"
   git config --global user.name "Your Name"
 
-  if [ "$ENV" == "vim72" ]; then
+  if [ "$ENV" == "vim74" ]; then
     mkdir -p ${DEPS}/bin
     ln -s /usr/bin/vim.nox ${DEPS}/bin/vim
     return