Add jdk configurations to Travis CI (#65)

* fix: (Travis) add jdk configurations to Travis CI

* fix: (Build) update plugin versions for JDK11 build

Author: igdianov

.travis.yml

@@ -1,6 +1,10 @@
 language: java
 sudo: required
 
+jdk:
+  - oraclejdk8
+  - openjdk11
+
 services:
   - docker
 

pom.xml

@@ -20,7 +20,10 @@
     <properties>
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
-
+        
+        <jacoco-maven-plugin.version>0.8.2</jacoco-maven-plugin.version>        
+        <maven-compiler-plugin.version>3.8.0</maven-compiler-plugin.version>
+        <maven-deploy-plugin.version>2.8.2</maven-deploy-plugin.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
 
@@ -101,7 +104,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-deploy-plugin</artifactId>
-                    <version>2.8.2</version>
+                    <version>${maven-deploy-plugin.version}</version>
                 </plugin>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
@@ -111,7 +114,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-compiler-plugin</artifactId>
-                    <version>3.1</version>
+                    <version>${maven-compiler-plugin.version}</version>
                 </plugin>
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
@@ -278,7 +281,7 @@
             <plugin>
                 <groupId>org.jacoco</groupId>
                 <artifactId>jacoco-maven-plugin</artifactId>
-                <version>0.7.9</version>
+                <version>${jacoco-maven-plugin.version}</version>
                 <executions>
                     <!-- Unit tests configuration -->
                     <execution>