Set minimum Java version to 8

Fixes #33

Author: acogoluegnes

pom.xml

@@ -48,7 +48,7 @@
     <awaitility.version>3.0.0</awaitility.version>
 
     <maven.dependency.plugin.version>2.8</maven.dependency.plugin.version>
-    <maven.compiler.plugin.version>3.5.1</maven.compiler.plugin.version>
+    <maven.compiler.plugin.version>3.7.0</maven.compiler.plugin.version>
     <maven.surefire.plugin.version>2.19.1</maven.surefire.plugin.version>
     <maven.failsafe.plugin.version>2.19.1</maven.failsafe.plugin.version>
     <maven.jar.plugin.version>3.0.2</maven.jar.plugin.version>
@@ -62,7 +62,7 @@
     <maven.javadoc.plugin.version>3.0.0-M1</maven.javadoc.plugin.version>
     <maven.gpg.plugin.version>1.6</maven.gpg.plugin.version>
 
-    <java.compile.version>1.6</java.compile.version>
+    <java.compile.version>1.8</java.compile.version>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 
     <surefire.reports.dir>target/surefire-reports</surefire.reports.dir>