upgrade gradle version for android studio 3, fix some lint warnings

app/build.gradle

@@ -2,7 +2,7 @@ apply plugin: 'com.android.application'
 
 android {
     compileSdkVersion 26
-    buildToolsVersion "26.0.1"
+    buildToolsVersion '26.0.2'
     defaultConfig {
         applicationId "com.keylesspalace.tusky"
         minSdkVersion 15
@@ -19,9 +19,15 @@ android {
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
         }
     }
+
+    flavorDimensions "store"
     productFlavors {
-        google {}
-        fdroid {}
+        google {
+            dimension "store"
+        }
+        fdroid {
+            dimension "store"
+        }
     }
     lintOptions {
         disable 'MissingTranslation'
@@ -60,7 +66,7 @@ dependencies {
 
     //room
     compile "android.arch.persistence.room:runtime:1.0.0-rc1"
-    annotationProcessor 'android.arch.persistence.room:compiler:1.0.0-beta2'
+    annotationProcessor 'android.arch.persistence.room:compiler:1.0.0-rc1'
 
     testCompile "junit:junit:4.12"
     androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {