Build files: targetCompatibility default is sourceCompatibility.

- Now unified across build files.

Author: greenrobot-team

objectbox-java-api/build.gradle

@@ -4,7 +4,6 @@ group = 'io.objectbox'
 version= rootProject.version
 
 sourceCompatibility = 1.7
-targetCompatibility = 1.7
 
 javadoc {
     failOnError = false

objectbox-java/build.gradle

@@ -1,12 +1,11 @@
 apply plugin: 'java'
 apply plugin: 'findbugs'
 
-targetCompatibility = '1.7'
-sourceCompatibility = '1.7'
-
 group = 'io.objectbox'
 version= rootProject.version
 
+sourceCompatibility = '1.7'
+
 tasks.withType(FindBugs) {
     reports {
         xml.enabled false