OmniSharp.exe.config should set 4.7.2 as the required framework version

[gregg-miskelly]

OmniSharp now requires 4.7.2, but OmniSharp.exe.config still has the required version set to 4.6.1. This should be changed so that Windows will display the upgrade prompt instead of failing in hard to understand ways.

From c:\Users\greggm.vscode\extensions\ms-vscode.csharp-1.19.0.omnisharp\1.32.18\OmniSharp.exe.config:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1" />
  </startup>
  <runtime>