Add explicit NDK version to keep CI stable and happy (#782)

CDRussell · web-flow · commit 7183ea2ed555 · 2020-04-20T12:56:21.000+01:00
diff --git a/app/build.gradle b/app/build.gradle
@@ -11,6 +11,7 @@ ext {
 
 android {
     compileSdkVersion 28
+    ndkVersion '21.0.6113669'
     defaultConfig {
         applicationId "com.duckduckgo.mobile.android"
         minSdkVersion 21
