Add java8 support

app/build.gradle

@@ -39,7 +39,7 @@ static def gitBranch() {
 
 android {
     compileSdkVersion 27
-    buildToolsVersion '27.0.0'
+    buildToolsVersion '27.0.2'
     dataBinding {
         enabled = true
     }
@@ -76,6 +76,10 @@ android {
         disable 'InvalidPackage'
         abortOnError false
     }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
 }
 
 ext {
@@ -83,8 +87,7 @@ ext {
 }
 
 dependencies {
-    implementation fileTree(dir: 'libs', include: ['*.jar'])
-
+    implementation fileTree(include: ['*.jar'], dir: 'libs')
     implementation "com.android.support:support-compat:$supportLibVersion"
     implementation "com.android.support:support-core-utils:$supportLibVersion"
     implementation "com.android.support:support-core-ui:$supportLibVersion"
@@ -101,7 +104,6 @@ dependencies {
     implementation "com.android.support:percent:$supportLibVersion"
     implementation "com.android.support:preference-v7:$supportLibVersion"
     implementation "com.android.support:preference-v14:$supportLibVersion"
-
     implementation 'com.github.kabouzeid:app-theme-helper:1.3.7'
     implementation 'com.github.kabouzeid:RecyclerView-FastScroll:1.0.16-kmod'
     implementation 'com.github.kabouzeid:SeekArc:1.2-kmod'
@@ -120,17 +122,13 @@ dependencies {
     implementation 'me.zhanghai.android.materialprogressbar:library:1.4.1'
     implementation 'org.eclipse.mylyn.github:org.eclipse.egit.github.core:2.1.5'
     implementation 'com.jakewharton:butterknife:8.6.0'
-
     implementation('com.h6ah4i.android.widget.advrecyclerview:advrecyclerview:0.11.0@aar') {
         transitive = true
     }
-
     implementation 'com.crashlytics.sdk.android:crashlytics:2.8.0'
     implementation('com.crashlytics.sdk.android:answers:1.3.13@aar') {
         transitive = true
     }
-
     testImplementation 'junit:junit:4.12'
-
     annotationProcessor 'com.jakewharton:butterknife-compiler:8.6.0'
 }