Fix nuspec format

***NO_CI***

nanoFramework.System.IO.Ports.nuspec

@@ -32,6 +32,6 @@
     <file src="assets\readme.txt" target="" />
     <file src="README.md" target="docs\" />
     <file src="assets\nf-logo.png" target="images" />
-    <file src="LICENSE.md" target="" /
+    <file src="LICENSE.md" target="" />
   </files>
-</package>
+</package>