Remove Version from Dropbox.Api.nuspec (#220)

Author: mtruong-dbx

dropbox-sdk-dotnet/Dropbox.Api/Dropbox.Api.nuspec

@@ -2,7 +2,6 @@
 <package>
   <metadata>
     <id>Dropbox.Api</id>
-    <version>5.7.0</version>
     <title>Dropbox v2 API</title>
     <authors>Dropbox</authors>
     <owners>Dropbox</owners>