Remove support for Java 8, update dependencies, improve CI & ReadMe

* Java 8: The TravisCI build is failing due to trying to run the build in MacOS with Java 8 (not supported)
* Dependencies: Updated the Junit to 5.3.2 and Gradle to 5.1.1

Author: JavierCane

build.gradle

@@ -1,14 +1,15 @@
 apply plugin: 'java'
 
-sourceCompatibility = 1.8
+sourceCompatibility = 1.11
+targetCompatibility = 1.11
 
 repositories {
     mavenCentral()
 }
 
 dependencies {
-    testCompile('org.junit.jupiter:junit-jupiter-api:5.2.0')
-    testRuntime('org.junit.jupiter:junit-jupiter-engine:5.2.0')
+    testCompile('org.junit.jupiter:junit-jupiter-api:5.3.2')
+    testRuntime('org.junit.jupiter:junit-jupiter-engine:5.3.2')
 }
 
 test {
@@ -21,9 +22,4 @@ test {
     reports {
         html.enabled = true
     }
-}
-
-task wrapper(type: Wrapper) {
-    description = 'Generates gradlew[.bat] scripts'
-    gradleVersion = '4.6'
 }

gradle/wrapper/gradle-wrapper.jar

@@ -1,6 +1,5 @@
-#Fri Jun 01 07:06:45 CEST 2018
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.1.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.10-all.zip