Build: upgrade to Java 1.8.

app/build.gradle

@@ -119,13 +119,16 @@ android {
     } else {
          buildTypes.release.signingConfig = null
     }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
 }
 
 dependencies {
     def acraVersion = '5.0.1'
     implementation "ch.acra:acra-mail:$acraVersion"
     implementation "ch.acra:acra-toast:$acraVersion"
-
     def supportVersion = '27.1.1'
     implementation "com.android.support:support-core-ui:$supportVersion"
     implementation "com.android.support:support-compat:$supportVersion"
@@ -134,30 +137,25 @@ dependencies {
     implementation "com.android.support:cardview-v7:$supportVersion"
     implementation "com.android.support:design:$supportVersion"
     implementation "com.android.support:preference-v14:$supportVersion"
-
     compile 'com.github.yukuku:ambilwarna:2.0.1'
-    compile ('com.github.worker8:tourguide:1.0.17-SNAPSHOT@aar'){
-         transitive=true
+    compile('com.github.worker8:tourguide:1.0.17-SNAPSHOT@aar') {
+        transitive = true
     }
-
     compile 'io.requery:requery:1.5.0'
     compile 'io.requery:requery-android:1.5.0'
     compile 'io.requery:requery-kotlin:1.5.0'
     kapt 'io.requery:requery-processor:1.5.0'
-
-    compile group: 'com.madgag.spongycastle', name: 'core', version: '1.54.0.0'
-    compile group: 'com.madgag.spongycastle', name: 'prov', version: '1.54.0.0'
-    compile group: 'com.google.code.gson', name: 'gson', version: '1.7.2'
+    compile 'com.madgag.spongycastle:core:1.54.0.0'
+    compile 'com.madgag.spongycastle:prov:1.54.0.0'
+    compile 'com.google.code.gson:gson:1.7.2'
     compile 'com.squareup.okhttp3:logging-interceptor:3.8.0'
     compile 'org.apache.commons:commons-collections4:4.1'
     compileOnly 'org.projectlombok:lombok:1.16.20'
     annotationProcessor 'org.projectlombok:lombok:1.16.20'
     compile 'net.cachapa.expandablelayout:expandablelayout:2.9.2'
-
     compile project(':cert4android')
     compile project(':ical4android')
     compile project(':vcard4android')
-
     // for tests
     androidTestCompile('com.android.support.test:runner:0.5') {
         exclude group: 'com.android.support', module: 'support-annotations'
@@ -167,7 +165,6 @@ dependencies {
     }
     androidTestCompile 'junit:junit:4.12'
     androidTestCompile 'com.squareup.okhttp3:mockwebserver:3.8.0'
-
     testCompile 'junit:junit:4.12'
     testCompile 'com.squareup.okhttp3:mockwebserver:3.8.0'
 }