[Fix] nvm_has_colors: also check if stdout is a terminal

test/fast/Set Colors/nvm_print_default_alias calls nvm_get_colors

@@ -11,6 +11,8 @@ die () {
 
 set -e
 
+nvm_has_colors() { return 0; }
+
 nvm_get_colors(){
     echo "0;95m"
 }

test/fast/Set Colors/nvm_print_versions calls nvm_get_colors

@@ -22,6 +22,8 @@ if [ -n ${NVM_COLORS} ]; then
   unset NVM_COLORS
 fi
 
+nvm_has_colors() { return 0; }
+
 # default system color
 nvm use system
 OUTPUT=$(nvm_print_versions system)