make submodule tracking a branch

.gitmodules

@@ -1,28 +1,36 @@
 [submodule "zsh/plugins/zsh-syntax-highlighting"]
 	path = zsh/plugins/zsh-syntax-highlighting
 	url = https://github.com/zsh-users/zsh-syntax-highlighting
+	branch = master
 [submodule "vim/bundle/undotree"]
 	path = vim/bundle/undotree
 	url = https://github.com/mbbill/undotree
 [submodule "vim/bundle/syntastic"]
 	path = vim/bundle/syntastic
 	url = https://github.com/scrooloose/syntastic
+	branch = master
 [submodule "vim/bundle/mru.vim"]
 	path = vim/bundle/mru.vim
 	url = https://github.com/vim-scripts/mru.vim
+	branch = master
 [submodule "vim/bundle/vim-fugitive"]
 	path = vim/bundle/vim-fugitive
 	url = https://github.com/tpope/vim-fugitive
+	branch = master
 [submodule "vim/bundle/vimux"]
 	path = vim/bundle/vimux
 	url = https://github.com/benmills/vimux
+	branch = master
 [submodule "vim/bundle/vim-airline"]
 	path = vim/bundle/vim-airline
 	url = https://github.com/vim-airline/vim-airline
+	branch = master
 [submodule "vim/bundle/YouCompleteMe"]
 	path = vim/bundle/YouCompleteMe
 	url = https://github.com/Valloric/YouCompleteMe
     ignore = dirty
+	branch = master
 [submodule "vim/bundle/rust.vim"]
 	path = vim/bundle/rust.vim
 	url = https://github.com/rust-lang/rust.vim
+	branch = master