fix: actually set 'husky_skip_init' as readonly (#1104)

Previously, the script would export the empty 'readonly' variable, along
with 'husky_skip_init' which has a value of 1. Now, the script sets
'husky_skip_init' to 1, and properly gives is the readonly and exported
attributes.

husky.sh

@@ -19,7 +19,8 @@ if [ -z "$husky_skip_init" ]; then
     . ~/.huskyrc
   fi
 
-  export readonly husky_skip_init=1
+  readonly husky_skip_init=1
+  export husky_skip_init
   sh -e "$0" "$@"
   exitCode="$?"