[Fix] Add autocompletion support to zsh

Fixes #1707.
diff --git a/test/install_script/nvm_detect_profile b/test/install_script/nvm_detect_profile
index ba5a6ea..1044659 100755
--- a/test/install_script/nvm_detect_profile
+++ b/test/install_script/nvm_detect_profile
@@ -14,6 +14,8 @@
   unset HOME
   unset NVM_ENV
   unset NVM_DETECT_PROFILE
+  unset BASH_VERSION
+  unset ZSH_VERSION
   unset -f setup cleanup die
   rm -f ".bashrc" ".bash_profile" ".zshrc" ".profile" "test_profile" > "/dev/null" 2>&1
 }
@@ -27,7 +29,7 @@
 #
 
 # .bashrc should be detected for bash
-NVM_DETECT_PROFILE="$(SHELL="/bin/bash"; unset PROFILE; nvm_detect_profile)"
+NVM_DETECT_PROFILE="$(BASH_VERSION="1"; unset PROFILE; nvm_detect_profile)"
 if [ "$NVM_DETECT_PROFILE" != "$HOME/.bashrc" ]; then
   die "nvm_detect_profile didn't pick \$HOME/.bashrc for bash"
 fi
@@ -39,7 +41,7 @@
 fi
 
 # .zshrc should be detected for zsh
-NVM_DETECT_PROFILE="$(SHELL="/usr/bin/zsh"; unset PROFILE; nvm_detect_profile)"
+NVM_DETECT_PROFILE="$(ZSH_VERSION="1"; unset PROFILE; unset BASH_VERSION; nvm_detect_profile)"
 if [ "$NVM_DETECT_PROFILE" != "$HOME/.zshrc" ]; then
   die "nvm_detect_profile didn't pick \$HOME/.zshrc for zsh"
 fi
@@ -56,7 +58,7 @@
 #
 
 # $PROFILE is a valid file
-NVM_DETECT_PROFILE="$(PROFILE="test_profile"; nvm_detect_profile)"
+NVM_DETECT_PROFILE="$(PROFILE="test_profile"; unset ZSH_VERSION; nvm_detect_profile)"
 if [ "$NVM_DETECT_PROFILE" != "test_profile" ]; then
   die "nvm_detect_profile didn't pick \$PROFILE when it was a valid file"
 fi
@@ -75,35 +77,35 @@
 #
 
 # It should favor .profile if file exists
-NVM_DETECT_PROFILE="$(unset SHELL; nvm_detect_profile)"
+NVM_DETECT_PROFILE="$(unset BASH_VERSION; unset ZSH_VERSION; nvm_detect_profile)"
 if [ "$NVM_DETECT_PROFILE" != "$HOME/.profile" ]; then
   die "nvm_detect_profile should have selected .profile"
 fi
 
 # Otherwise, it should favor .bashrc if file exists
 rm ".profile"
-NVM_DETECT_PROFILE="$(unset SHELL; nvm_detect_profile)"
+NVM_DETECT_PROFILE="$(unset BASH_VERSION; unset ZSH_VERSION; nvm_detect_profile)"
 if [ "$NVM_DETECT_PROFILE" != "$HOME/.bashrc" ]; then
   die "nvm_detect_profile should have selected .bashrc"
 fi
 
 # Otherwise, it should favor .bash_profile if file exists
 rm ".bashrc"
-NVM_DETECT_PROFILE="$(unset SHELL; nvm_detect_profile)"
+NVM_DETECT_PROFILE="$(unset BASH_VERSION; unset ZSH_VERSION; nvm_detect_profile)"
 if [ "$NVM_DETECT_PROFILE" != "$HOME/.bash_profile" ]; then
   die "nvm_detect_profile should have selected .bash_profile"
 fi
 
 # Otherwise, it should favor .zshrc if file exists
 rm ".bash_profile"
-NVM_DETECT_PROFILE="$(unset SHELL; nvm_detect_profile)"
+NVM_DETECT_PROFILE="$(unset BASH_VERSION; unset ZSH_VERSION; nvm_detect_profile)"
 if [ "$NVM_DETECT_PROFILE" != "$HOME/.zshrc" ]; then
   die "nvm_detect_profile should have selected .zshrc"
 fi
 
 # It should be empty if none is found
 rm ".zshrc"
-NVM_DETECT_PROFILE="$(unset SHELL; nvm_detect_profile)"
+NVM_DETECT_PROFILE="$(unset BASH_VERSION; unset ZSH_VERSION; nvm_detect_profile)"
 if [ ! -z "$NVM_DETECT_PROFILE" ]; then
   die "nvm_detect_profile should have returned an empty value"
 fi