specify cmake version 3.6 or later

android/build.gradle

@@ -42,6 +42,8 @@ android {
         // Encapsulates your CMake build configurations.
         cmake {
             //version "3.10.2"
+            // f-droid uses 3.7, let's hope it works this way.
+            version "3.6.0+"
             // Provides a relative path to your CMake build script.
             path "CMakeLists.txt"
         }