Fix typo in docs
Fix typo in docs

(Change pushed to gh-pages already)
jskeet/google-cloud-dotnet,jskeet/google-cloud-dotnet,jskeet/google-cloud-dotnet,evildour/google-cloud-dotnet,jskeet/google-cloud-dotnet,iantalarico/google-cloud-dotnet,jskeet/gcloud-dotnet,evildour/google-cloud-dotnet,iantalarico/google-cloud-dotnet,jskeet/google-cloud-dotnet,evildour/google-cloud-dotnet,googleapis/google-cloud-dotnet,googleapis/google-cloud-dotnet,iantalarico/google-cloud-dotnet,googleapis/google-cloud-dotnet