patch up zshrc to work on other computers

dotfiles/zsh/exports.zsh

@@ -29,5 +29,10 @@ export HISTCONTROL=ignoredups
 # If go is installed, set the $GOPATH to the projects directory created above.
 if which go > /dev/null; then export GOPATH=$HOME/.go; fi
 	
-export PATH="$PATH:$HOME/.rvm/bin"
-. "$HOME/.cargo/env"
+if [ -d "$HOME/.rvm" ]; then
+	export PATH="$PATH:$HOME/.rvm/bin"
+fi
+
+if [ -f "$HOME/.cargo/env" ]; then
+	. "$HOME/.cargo/env"
+fi

dotfiles/zsh/zshrc

@@ -59,20 +59,21 @@ if [[ ! -d $HOME/.zsh ]]; then
   popd
 fi
 
-# Install zsh-syntax-highlighting if it doesn't exist
-if [[ ! -d $HOME/.zsh/zsh-syntax-highlighting ]]; then 
-  if ! is-at-least 4.3.11; then
-    echo "ZSH syntax highlighting requires ZSH >= 4.3.11 (current: $ZSH_VERSION)."
-  else
-    echo "Installing zsh syntax highlighting"
-    pushd
-    
-    cd $HOME/.zsh
-    git clone https://github.com/zsh-users/zsh-syntax-highlighting.git 
-
-    popd
-  fi
+autoload -U is-at-least
 
+# Install zsh-syntax-highlighting if it doesn't exist
+if is-at-least 4.3.11; then
+	if [[ ! -d $HOME/.zsh/zsh-syntax-highlighting ]]; then 
+	    echo "Installing zsh syntax highlighting"
+	    pushd
+	    
+	    cd $HOME/.zsh
+	    git clone https://github.com/zsh-users/zsh-syntax-highlighting.git 
+
+	    popd
+  	fi
+else
+	echo "ZSH syntax highlighting requires ZSH >= 4.3.11 (current: $ZSH_VERSION)."
 fi 
 
 zstyle ':completion:*:*:git:*' script $HOME/.zsh/git-completion.bash