Upgrade NEST Test version to support elastic 7

Author: EngRslan

test/WorkflowCore.Tests.Elasticsearch/WorkflowCore.Tests.Elasticsearch.csproj

@@ -8,7 +8,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
-    <PackageReference Include="NEST" Version="7.5.1" />
+    <PackageReference Include="NEST" Version="7.14.1" />
     <PackageReference Include="xunit" Version="2.4.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
   </ItemGroup>