app: Upgrade to build tools version 27.0.3

Signed-off-by: Samuel Holland <samuel@sholland.org>

app/build.gradle

@@ -1,7 +1,7 @@
 apply plugin: 'com.android.application'
 
 android {
-    buildToolsVersion '27.0.2'
+    buildToolsVersion '27.0.3'
     buildTypes {
         release {
             minifyEnabled false