Add the xml namespace to work with MSBuild v14

This fixes #1823.

Author: jbaehr

src/GitVersionTask/build/GitVersionTask.props

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
     <PropertyGroup>
         <GitVersionAssemblyFile Condition="$(GitVersionAssemblyFile) == '' And '$(MSBuildRuntimeType)' != 'Core'">$(MSBuildThisFileDirectory)..\tools\net472\GitVersionTask.MsBuild.dll</GitVersionAssemblyFile>
         <GitVersionAssemblyFile Condition="$(GitVersionAssemblyFile) == '' And '$(MSBuildRuntimeType)' == 'Core'">$(MSBuildThisFileDirectory)..\tools\netstandard2.0\GitVersionTask.MsBuild.dll</GitVersionAssemblyFile>

src/GitVersionTask/build/GitVersionTask.targets

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
     <UsingTask TaskName="GetVersion" AssemblyFile="$(GitVersionAssemblyFile)"/>
     <UsingTask TaskName="GenerateGitVersionInformation" AssemblyFile="$(GitVersionAssemblyFile)"/>
     <UsingTask TaskName="UpdateAssemblyInfo" AssemblyFile="$(GitVersionAssemblyFile)" />

src/GitVersionTask/buildMultiTargeting/GitVersionTask.props

@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
     <Import Project="$(MSBuildThisFileDirectory)..\build\$(MSBuildThisFile)"/>
 </Project>

src/GitVersionTask/buildMultiTargeting/GitVersionTask.targets

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
     <UsingTask TaskName="GetVersion" AssemblyFile="$(GitVersionAssemblyFile)"/>
     <UsingTask TaskName="WriteVersionInfoToBuildLog" AssemblyFile="$(GitVersionAssemblyFile)" />