[chore] Release 2.0.0 (#270)

Author: hiranya911

FirebaseAdmin/FirebaseAdmin/FirebaseAdmin.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <Version>1.17.1</Version>
+    <Version>2.0.0</Version>
     <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netstandard2.0</TargetFrameworks>
     <LangVersion>latest</LangVersion>