Fix failed callbacks

To use this release, you must download the aar file attached to this release, and configure it with your project like so:

• Edit your outermost build.gradle file to add an libs entry like so:

     allprojects {
         repositories {
             google()
             jcenter()
             flatDir {
                 dirs 'libs'
             }
         }
     }

• Edit your innermost build.gradle file to add the beta library AAR as a dependency like so:

dependencies {
    implementation 'org.altbeacon:android-beacon-library:2.16.2-beta1@aar'
}

• Create a /libs folder next to the innermost build.gradle above, then download and copy the aar file attached to this release into this folder.