Drop Java 7 support

It is EOL and not supported on Travis anymore. Intead, test against Java 11

Author: slonopotamus

.travis.yml

@@ -3,8 +3,8 @@
 #
 language: java
 jdk:
-  - oraclejdk8
-  - oraclejdk7
+  - openjdk8
+  - openjdk11
 before_install:
   # ensure gradlew has proper permission
   - chmod a+x ./gradlew

pom.xml

@@ -326,7 +326,7 @@
         </repository>
     </distributionManagement>
     <properties>
-        <java.version>1.7</java.version>
+        <java.version>1.8</java.version>
         <maven.compiler.source>${java.version}</maven.compiler.source>
         <maven.compiler.target>${java.version}</maven.compiler.target>
         <gson-fire-version>1.8.0</gson-fire-version>