Change JVM compilation target from 1.8 to 1.6

This lets Android apps to use the library.
Also, upgrade Kotlin to v1.2.60.

build.gradle

@@ -1,12 +1,12 @@
 buildscript {
-    ext.kotlin_version = '1.1.51'
+    ext.kotlin_version = '1.2.60'
 
     repositories {
         google()
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.0.0'
+        classpath 'com.android.tools.build:gradle:3.0.1'
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
         classpath 'com.github.dcendents:android-maven-gradle-plugin:2.0'
         classpath 'com.palantir:jacoco-coverage:0.4.0'
@@ -20,4 +20,4 @@ allprojects {
     }
 }
 
-apply plugin: 'com.palantir.jacoco-full-report'
+apply plugin: 'com.palantir.jacoco-full-report'

time-android/build.gradle

@@ -33,6 +33,6 @@ android {
 
 dependencies {
     implementation fileTree(dir: 'libs', include: ['*.jar'])
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
     implementation project(':time')
 }

time/build.gradle

@@ -6,13 +6,13 @@ group = 'com.github.kizitonwose'
 
 dependencies {
     implementation fileTree(dir: 'libs', include: ['*.jar'])
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
     testImplementation 'junit:junit:4.12'
 }
 
 compileKotlin {
-    kotlinOptions.jvmTarget = "1.8"
+    kotlinOptions.jvmTarget = "1.6"
 }
 compileTestKotlin {
-    kotlinOptions.jvmTarget = "1.8"
+    kotlinOptions.jvmTarget = "1.6"
 }