IDEA，与gradle引入jar包报错

Warning:<i><b>root project ‘netty_lecture‘: Unable to resolve additional project configuration.</b>
Details: org.gradle.api.internal.artifacts.ivyservice.DefaultLenientConfiguration$ArtifactResolveException: Could not resolve all files for configuration ‘:compileClasspath‘.
Caused by: org.gradle.internal.resolve.ArtifactResolveException: Could not download protobuf-java.jar (com.google.protobuf:protobuf-java:3.5.1)
Caused by: org.gradle.api.resources.ResourceException: Could not get resource ‘https://repo.maven.apache.org/maven2/com/google/protobuf/protobuf-java/3.5.1/protobuf-java-3.5.1.jar‘.
Caused by: java.net.SocketTimeoutException: Read timed out</i>

group ‘com.jiangdashuai‘
version ‘1.0‘

apply plugin: ‘java‘

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
//    testCompile group: ‘junit‘, name: ‘junit‘, version: ‘4.12‘
    compile(
             ‘io.netty:netty-all:4.1.19.Final‘,
            ‘com.google.protobuf:protobuf-java:3.5.1‘,
            ‘com.google.protobuf:protobuf-lite:3.0.1‘
    )
}

apply plugin: ‘java‘

apply plugin: ‘java‘
apply plugin: ‘idea‘