feat(half-life): add virtualenv prompt (#11708)

Closes #11709

lib/functions.zsh

@@ -5,7 +5,7 @@ function zsh_stats() {
 }
 
 function uninstall_oh_my_zsh() {
-  env ZSH="$ZSH" sh "$ZSH/tools/uninstall.sh"
+  command env ZSH="$ZSH" sh "$ZSH/tools/uninstall.sh"
 }
 
 function upgrade_oh_my_zsh() {

themes/half-life.zsh-theme

@@ -89,5 +89,9 @@ ZSH_THEME_RUBY_PROMPT_PREFIX="with%F{red} "
 ZSH_THEME_RUBY_PROMPT_SUFFIX="%{$reset_color%}"
 ZSH_THEME_RVM_PROMPT_OPTIONS="v g"
 
+# virtualenv prompt settings
+ZSH_THEME_VIRTUALENV_PREFIX=" with%F{red} "
+ZSH_THEME_VIRTUALENV_SUFFIX="%{$reset_color%}"
+
 setopt prompt_subst
-PROMPT="${purple}%n%{$reset_color%} in ${limegreen}%~%{$reset_color%}\$(ruby_prompt_info)\$vcs_info_msg_0_${orange} λ%{$reset_color%} "
+PROMPT="${purple}%n%{$reset_color%} in ${limegreen}%~%{$reset_color%}\$(virtualenv_prompt_info)\$(ruby_prompt_info)\$vcs_info_msg_0_${orange} λ%{$reset_color%} "