Workaround install crash on Android 5 and below

The aapt2 tool, new to Android Studio 3, creates an APK which fails
to install on Android 5 and below if it contains the following bug:

  https://issuetracker.google.com/issues/64434571

Build tools 27.0.1 has a mitigation. Avoiding aapt2 also avoids hitting
the bug.

gradle.properties

@@ -0,0 +1,23 @@
+# Project-wide Gradle settings.
+
+# IDE (e.g. Android Studio) users:
+# Gradle settings configured through the IDE *will override*
+# any settings specified in this file.
+
+# For more details on how to configure your build environment visit
+# http://www.gradle.org/docs/current/userguide/build_environment.html
+
+# Specifies the JVM arguments used for the daemon process.
+# The setting is particularly useful for tweaking memory settings.
+# Default value: -Xmx10248m -XX:MaxPermSize=256m
+# org.gradle.jvmargs=-Xmx2048m -XX:MaxPermSize=512m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8
+
+# When configured, Gradle will run in incubating parallel mode.
+# This option should only be used with decoupled projects. More details, visit
+# http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
+# org.gradle.parallel=true
+
+# The aapt2 tool creates an APK which fails to install on Android 5 and below if it contains
+# a bug. Build tools 27.0.1 has a mitigation. Avoiding aapt2 also avoids hitting the bug.
+# See: https://issuetracker.google.com/issues/64434571
+android.enableAapt2=false