Update Atmosphere runtime to 2.1.2.vaadin3 (#13971)

Atmosphere 2.1.2.vaadin3 includes fix for:
https://github.com/Atmosphere/atmosphere/issues/1643

Change-Id: I67c07dc3b32ebb3b0eed634bf143bac9a7e5efe2

push/build.xml

     <property name="vaadinPush.debug.js" location="${result.dir}/js/VAADIN/vaadinPush.debug.js" />
 
     <!-- Keep the version number in sync with ivy.xml, server/src/com/vaadin/server/Constants.java -->
-    <property name="atmosphere.runtime.version" value="2.1.2.vaadin2" />
+    <property name="atmosphere.runtime.version" value="2.1.2.vaadin3" />
     <property name="jquery.js" location="lib/jquery/jquery-1.11.0.js" />
 
     <path id="classpath.compile.custom" />

push/ivy.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE ivy-module [
 <!-- Keep the version number in sync with build.xml -->
-    <!ENTITY atmosphere.runtime.version "2.1.2.vaadin2">
+    <!ENTITY atmosphere.runtime.version "2.1.2.vaadin3">
 
     <!ENTITY atmosphere.js.version "2.1.5.vaadin4">
 ]>

server/src/com/vaadin/server/Constants.java

 
     // Keep the version number in sync with push/build.xml and other locations
     // listed in that file
-    static final String REQUIRED_ATMOSPHERE_RUNTIME_VERSION = "2.1.2.vaadin2";
+    static final String REQUIRED_ATMOSPHERE_RUNTIME_VERSION = "2.1.2.vaadin3";
 
     static final String INVALID_ATMOSPHERE_VERSION_WARNING = "\n"
             + "=================================================================\n"