chore: Use gradle variables

app/build.gradle

@@ -39,10 +39,15 @@ android {
     }
 }
 
+ext {
+    roomVersion = '1.1.1'
+    archLifecycleVersion = '1.1.1'
+}
+
 dependencies {
     // region Kotlin
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
-    kapt "android.arch.lifecycle:compiler:1.1.1"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlinVersion"
+    kapt "android.arch.lifecycle:compiler:$archLifecycleVersion"
     // endregion
 
     // region Support Library
@@ -52,17 +57,18 @@ dependencies {
     // endregion
 
     // region ViewModel and LiveData
-    implementation "android.arch.lifecycle:extensions:1.1.1"
+    implementation "android.arch.lifecycle:extensions:$archLifecycleVersion"
+    kapt "android.arch.lifecycle:compiler:$archLifecycleVersion"
     // alternatively, just ViewModel
-    //implementation "android.arch.lifecycle:viewmodel:1.1.0"
+    //implementation "android.arch.lifecycle:viewmodel:$archLifecycleVersion"
     // alternatively, just LiveData
-    //implementation "android.arch.lifecycle:livedata:1.1.0"
+    //implementation "android.arch.lifecycle:livedata:$archLifecycleVersion"
     // endregion
 
     // region Jetpack / Developer Experience
     // Room
-    implementation "android.arch.persistence.room:runtime:1.1.1"
-    kapt "android.arch.persistence.room:compiler:1.1.1"
+    implementation "android.arch.persistence.room:runtime:$roomVersion"
+    kapt "android.arch.persistence.room:compiler:$roomVersion"
 
     // Paging
     implementation "android.arch.paging:runtime:1.0.1"
@@ -79,6 +85,6 @@ dependencies {
     testImplementation "android.arch.core:core-testing:1.1.1"
 
     // Test helpers for Room
-    testImplementation "android.arch.persistence.room:testing:1.1.1"
+    testImplementation "android.arch.persistence.room:testing:$roomVersion"
     // endregion
 }

build.gradle

@@ -18,14 +18,14 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
-    ext.kotlin_version = '1.3.0'
+    ext.kotlinVersion = '1.3.0'
     repositories {
         google()
         jcenter()
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:3.3.1'
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files