scripts: Update NuGet package spec

Migrate from licenseUrl to license since licenseUrl is deprecated and
fix grammar for VS version list.

scripts/nuget/pugixml.nuspec

@@ -7,12 +7,12 @@
     <authors>Arseny Kapoulkine</authors>
     <owners>Arseny Kapoulkine</owners>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
-    <licenseUrl>https://pugixml.org/license.html</licenseUrl>
+    <license type="expression">MIT</license>
     <projectUrl>https://pugixml.org/</projectUrl>
     <iconUrl>https://github.com/zeux/pugixml/logo.svg</iconUrl>
     <description>pugixml is a C++ XML processing library, which consists of a DOM-like interface with rich traversal/modification capabilities, an extremely fast XML parser which constructs the DOM tree from an XML file/buffer, and an XPath 1.0 implementation for complex data-driven tree queries. Full Unicode support is also available, with Unicode interface variants and conversions between different Unicode encodings (which happen automatically during parsing/saving).
 pugixml is used by a lot of projects, both open-source and proprietary, for performance and easy-to-use interface.
-This package contains builds for VS2013, VS2015 and VS2017, VS2019, for both statically linked and DLL CRT; you can switch the CRT linkage in Project -> Properties -> Referenced Packages -> pugixml.</description>
+This package contains builds for VS2013, VS2015, VS2017 and VS2019, for both statically linked and DLL CRT; you can switch the CRT linkage in Project -> Properties -> Referenced Packages -> pugixml.</description>
     <summary>Light-weight, simple and fast XML parser for C++ with XPath support</summary>
     <releaseNotes>https://pugixml.org/docs/manual.html#changes</releaseNotes>
     <copyright>Copyright (c) 2006-2019 Arseny Kapoulkine</copyright>