update ndk / gradle in the "android-camera-permissions" OF branch?

[ofZach]

hi! just trying to setup things using this excellent guide:

https://medium.com/@ire_alva/getting-started-with-openframeworks-on-android-5202b92f6582

and your readme -- it seems like android-camera-permissions is a bit behind -- the ndk-verify.gradle refers to 12:

if(!ndkProperties.getProperty("Pkg.Revision").startsWith("12.1")) {
    throw new GradleException("Wrong version of NDK library found. Found version " + ndkProperties.getProperty("Pkg.Revision") +
            ", but openFrameworks requires version r12b")
}

but I think (not sure!) it needs to be updated to 15 (as Irene's tutorial / github master) refers to..