- updated kotlin version

- added dtmf input for outbound calls
- volume/speaker experiments

build.gradle

@@ -1,13 +1,13 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
-    ext.kotlin_version = '1.2.31'
+    ext.kotlin_version = '1.2.40'
     repositories {
         jcenter()
         google()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.1.0'
+        classpath 'com.android.tools.build:gradle:3.1.2'
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
 
         // NOTE: Do not place your application dependencies here; they belong