Update license to MIT (#516)

* Update license to MIT

* Add license text to .editorconfig for the future

* Make the editorconfig have the correct text

Author: tlmii

.editorconfig

@@ -21,6 +21,8 @@ insert_final_newline = true
 indent_size = 4
 dotnet_sort_system_directives_first = true:warning
 
+file_header_template = Licensed to the .NET Foundation under one or more agreements.\nThe .NET Foundation licenses this file to you under the MIT license.\nSee the License.txt file in the project root for more information.
+
 # Xml project files
 [*.{*proj,vcxproj.filters,projitems}]
 indent_size = 2

Directory.Build.props

@@ -16,6 +16,6 @@
 
   <PropertyGroup Condition="'$(CopyrightNetFoundation)' != ''">
     <Copyright>$(CopyrightMicrosoft)</Copyright>
-    <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
   </PropertyGroup>
 </Project>