Added Proguard rules for the library (rxJava)

Summary: #104

Reviewers: michal.zielinski, pawel.urban

Reviewed By: pawel.urban

Differential Revision: https://phabricator.polidea.com/D1987

dependencies.gradle

@@ -1,14 +1,16 @@
 ext {
     supportVersion = '25.0.0'
     buildToolsVersionVariable = "25.0.0"
+    rxJavaVersion = '1.2.3'
     sourceCompatibilityVersion = JavaVersion.VERSION_1_8
     targetCompatibilityVersion = JavaVersion.VERSION_1_8
     libs = [
             /* Application dependencies */
             retrolambda        : 'net.orfjackal.retrolambda:retrolambda:2.3.0',
             support            : "com.android.support:support-v4:$supportVersion",
             support_annotations: "com.android.support:support-annotations:$supportVersion",
-            rxjava             : 'io.reactivex:rxjava:1.2.2',
+            rxjava             : ["io.reactivex:rxjava:$rxJavaVersion",
+                                  "com.artemzin.rxjava:proguard-rules:$rxJavaVersion.+"],
             rxandroid          : 'io.reactivex:rxandroid:1.2.1',
             junit              : 'junit:junit:4.12',
             groovy             : 'org.codehaus.groovy:groovy:2.4.7:grooid',

rxandroidble/proguard-rules.pro

@@ -15,3 +15,6 @@
 #-keepclassmembers class fqcn.of.javascript.interface.for.webview {
 #   public *;
 #}
+
+# hide warnings caused by Retrolamdba
+-dontwarn java.lang.invoke.*