diff --git a/.travis.yml b/.travis.yml
index be71df4a..ebb2a811 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,6 +18,7 @@
 sudo: required
 group: deprecated-2017Q3
 language: scala
+jdk: openjdk8
 scala:
 - 2.12.7
 services:
diff --git a/core/java8/proxy/gradle/wrapper/gradle-wrapper.properties b/core/java8/proxy/gradle/wrapper/gradle-wrapper.properties
index 5d28e48e..d475d272 100644
--- a/core/java8/proxy/gradle/wrapper/gradle-wrapper.properties
+++ b/core/java8/proxy/gradle/wrapper/gradle-wrapper.properties
@@ -14,9 +14,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.6-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.5.1-bin.zip
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index 5d28e48e..d475d272 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -14,9 +14,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.6-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.5.1-bin.zip