Add jacoco for code coverage. (#42)

Signed-off-by: Pan Li <panli@microsoft.com>

.travis.yml

@@ -4,8 +4,12 @@ jdk:
 
 script:
   - mvn clean install
+  - mvn clean test
 
 cache:
   directories:
   - $HOME/.m2
 
+after_success:
+  - bash <(curl -s https://codecov.io/bash)
+

pom.xml

@@ -160,7 +160,7 @@
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-surefire-plugin</artifactId>
                     <configuration>
-                        <argLine>-Xms512m -Xmx512m</argLine>
+                        <argLine>${argLine} -Xms512m -Xmx512m</argLine>
                     </configuration>
                 </plugin>
             </plugins>
@@ -200,6 +200,29 @@
                     </archive>
                 </configuration>
             </plugin>
+
+            <plugin>
+                <groupId>org.jacoco</groupId>
+                <artifactId>jacoco-maven-plugin</artifactId>
+                <version>0.8.1</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>prepare-agent</goal>
+                        </goals>
+                    </execution>
+                    <execution>
+                        <id>report</id>
+                        <phase>test</phase>
+                        <goals>
+                            <goal>report</goal>
+                        </goals>
+                        <configuration>
+                            <outputDirectory>target/jacoco-report</outputDirectory>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
     </build>