fix: Turtle.get_Stroke defaulting to currentcolor ( Fixes #15 )

Fixing case

Author: James Brundage

Types/Turtle/get_Stroke.ps1

@@ -1,5 +1,5 @@
 if ($this.'.Stroke') {
     return $this.'.Stroke'
 } else {
-    return 'currentColor'
+    return 'currentcolor'
 }