Bump System.Text.Encodings.Web from 4.7.0 to 4.7.2 in /Source/MDK (#241)

Bumps [System.Text.Encodings.Web](https://github.com/dotnet/corefx) from 4.7.0 to 4.7.2.
- [Release notes](https://github.com/dotnet/corefx/releases)
- [Commits](https://github.com/dotnet/corefx/commits)

---
updated-dependencies:
- dependency-name: System.Text.Encodings.Web
  dependency-type: direct:production
...

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Source/MDK/packages.config

@@ -97,7 +97,7 @@
   <package id="System.Text.Encoding" version="4.3.0" targetFramework="net472" />
   <package id="System.Text.Encoding.CodePages" version="4.5.1" targetFramework="net472" />
   <package id="System.Text.Encoding.Extensions" version="4.3.0" targetFramework="net472" />
-  <package id="System.Text.Encodings.Web" version="4.7.0" targetFramework="net472" />
+  <package id="System.Text.Encodings.Web" version="4.7.2" targetFramework="net472" />
   <package id="System.Text.Json" version="4.7.0" targetFramework="net472" />
   <package id="System.Threading" version="4.3.0" targetFramework="net472" />
   <package id="System.Threading.Tasks" version="4.3.0" targetFramework="net472" />