In my pom.xml:

    <dependency>
      <groupId>com.google.cloud</groupId>
      <artifactId>google-cloud-pubsub</artifactId>
      <version>0.17.1-alpha</version>
    </dependency>
    <dependency>
      <groupId>com.google.cloud</groupId>
      <artifactId>google-cloud-datastore</artifactId>
      <version>1.0.0</version>
    </dependency>

Errors:

[ERROR] Failed to execute goal on project flexible-pubsub:
Could not resolve dependencies for project
com.example.flexible:flexible-pubsub:war:1.0-SNAPSHOT: Failed to collect dependencies for com.example.flexible:flexible-pubsub:war:1.0-SNAPSHOT: Could not resolve version conflict among [com.google.cloud:google-cloud-pubsub:jar:0.17.1-alpha -> com.google.cloud:google-cloud-core-grpc:jar:1.0.0 -> io.grpc:grpc-protobuf:jar:1.2.0 -> io.grpc:grpc-core:jar:1.2.0, com.google.cloud:google-cloud-pubsub:jar:0.17.1-alpha -> com.google.cloud:google-cloud-core-grpc:jar:1.0.0 -> io.grpc:grpc-protobuf:jar:1.2.0 -> io.grpc:grpc-protobuf-lite:jar:1.2.0 -> io.grpc:grpc-core:jar:1.2.0, com.google.cloud:google-cloud-pubsub:jar:0.17.1-alpha -> io.grpc:grpc-netty:jar:1.2.0 -> io.grpc:grpc-core:jar:[1.2.0,1.2.0], com.google.cloud:google-cloud-pubsub:jar:0.17.1-alpha -> io.grpc:grpc-stub:jar:1.2.0 -> io.grpc:grpc-core:jar:1.2.0, com.google.cloud:google-cloud-pubsub:jar:0.17.1-alpha -> io.grpc:grpc-auth:jar:1.2.0 -> io.grpc:grpc-core:jar:[1.2.0,1.2.0], com.google.cloud:google-cloud-datastore:jar:1.0.0 -> com.google.cloud.datastore:datastore-v1-protos:jar:1.3.0 -> com.google.api.grpc:grpc-google-common-protos:jar:0.1.0 -> io.grpc:grpc-all:jar:1.0.1 -> io.grpc:grpc-protobuf-nano:jar:1.0.1 -> io.grpc:grpc-core:jar:1.0.1, com.google.cloud:google-cloud-datastore:jar:1.0.0 -> com.google.cloud.datastore:datastore-v1-protos:jar:1.3.0 -> com.google.api.grpc:grpc-google-common-protos:jar:0.1.0 -> io.grpc:grpc-all:jar:1.0.1 -> io.grpc:grpc-core:jar:[1.0.1,1.0.1], com.google.cloud:google-cloud-datastore:jar:1.0.0 -> com.google.cloud.datastore:datastore-v1-protos:jar:1.3.0 -> com.google.api.grpc:grpc-google-common-protos:jar:0.1.0 -> io.grpc:grpc-all:jar:1.0.1 -> io.grpc:grpc-okhttp:jar:1.0.1 -> io.grpc:grpc-core:jar:[1.0.1,1.0.1]] -> [Help 1]