(#2893) Switch Unit and Integration tests to langVersion 7.3

This is to allow Visual Studio 2017 to build the project.
Otherwise, code in the FluentAssertions library will cause errors when build with VS2017.

Author: TheCakeIsNaOH

src/chocolatey.tests.integration/chocolatey.tests.integration.csproj

@@ -13,6 +13,7 @@
     <RootNamespace>chocolatey.tests.integration</RootNamespace>
     <AssemblyName>chocolatey.tests.integration</AssemblyName>
     <TargetFrameworkVersion>v4.8</TargetFrameworkVersion>
+    <LangVersion>7.3</LangVersion>
     <FileAlignment>512</FileAlignment>
     <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\</SolutionDir>
     <OverwriteReadOnlyFiles>true</OverwriteReadOnlyFiles>

src/chocolatey.tests/chocolatey.tests.csproj

@@ -13,6 +13,7 @@
     <RootNamespace>chocolatey.tests</RootNamespace>
     <AssemblyName>chocolatey.tests</AssemblyName>
     <TargetFrameworkVersion>v4.8</TargetFrameworkVersion>
+    <LangVersion>7.3</LangVersion>
     <FileAlignment>512</FileAlignment>
     <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\</SolutionDir>
     <TargetFrameworkProfile />