Android: Stick with buildToolsVersion 28.0.3

On Windows buildToolsVersion 29.0.0 have problems, therefore,
it's better to use a version that we know it works on all platofrms.

Change-Id: I25cdea4b8101bfe5f022025fcd7cc4cbf358fa03
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/android/templates/build.gradle

@@ -36,7 +36,7 @@ android {
 
     compileSdkVersion androidCompileSdkVersion.toInteger()
 
-    buildToolsVersion androidBuildToolsVersion
+    buildToolsVersion '28.0.3'
 
     sourceSets {
         main {