Update install commands to use && instead of ;

This way, if mkdir or cd fails, it'll stop rather than continuing to download or clone in the wrong directory.

Author: koalaman

README.markdown

@@ -8,7 +8,7 @@ private directories.
 
 Install to `~/.vim/autoload/pathogen.vim`. Or copy and paste:
 
- mkdir -p ~/.vim/autoload ~/.vim/bundle; \
+ mkdir -p ~/.vim/autoload ~/.vim/bundle && \
  curl -LSso ~/.vim/autoload/pathogen.vim https://tpo.pe/pathogen.vim
 
 If you're using Windows, change all occurrences of `~/.vim` to `~\vimfiles`.
@@ -30,7 +30,7 @@ Now any plugins you wish to install can be extracted to a subdirectory
 under `~/.vim/bundle`, and they will be added to the `'runtimepath'`.
 Observe:
 
- cd ~/.vim/bundle
+ cd ~/.vim/bundle && \
  git clone git://github.com/tpope/vim-sensible.git
 
 Now [sensible.vim](https://github.com/tpope/vim-sensible) is installed.