Update Datastore example to avoid build/run problems on Linux.

NSString.init(contentsOfFile:usedEncoding:) is not available (yet)
on Linux, and is used by String.init(contentsOfFile:). We replace
these calls with calls to String.init(contentsOfFile:,encoding:)

Examples/Datastore/PackageManager/Package.swift

@@ -18,7 +18,7 @@ let package = Package (
     name: "Datastore",
     dependencies: [
         .Package(url: "https://github.com/grpc/grpc-swift.git", Version(0,1,13)),
-        .Package(url: "https://github.com/apple/swift-protobuf.git", Version(0,9,901)),
-	.Package(url: "https://github.com/google/auth-library-swift.git", Version(0,2,0)),
+        .Package(url: "https://github.com/apple/swift-protobuf.git", Version(0,9,903)),
+        .Package(url: "https://github.com/google/auth-library-swift.git", Version(0,2,2)),
     ]
 )

Examples/Datastore/PackageManager/Sources/main.swift

@@ -45,7 +45,7 @@ guard let authToken = tokenProvider.token?.accessToken else {
 let projectID = "<YOUR PROJECT ID>"
 
 let certificateURL = URL(fileURLWithPath:"roots.pem")
-let certificates = try! String(contentsOf: certificateURL)
+let certificates = try! String(contentsOf: certificateURL, encoding: .utf8)
 let service = Google_Datastore_V1_DatastoreService(address:"datastore.googleapis.com",
                                                    certificates:certificates,
                                                    host:nil)
@@ -53,7 +53,7 @@ let service = Google_Datastore_V1_DatastoreService(address:"datastore.googleapis
 service.metadata = Metadata(["authorization":"Bearer " + authToken])
 
 var request = Google_Datastore_V1_RunQueryRequest()
-request.projectId = projectID
+request.projectID = projectID
 
 var query = Google_Datastore_V1_GqlQuery()
 query.queryString = "select *"