Bump up default User-Agent HTTP header value (AsyncHttpClient#1399)

Change from AHC/2.0 to AHC/2.1

Author: twz123

client/src/main/resources/ahc-default.properties

@@ -10,7 +10,7 @@ org.asynchttpclient.connectionTtl=-1
 org.asynchttpclient.followRedirect=false
 org.asynchttpclient.maxRedirects=5
 org.asynchttpclient.compressionEnforced=false
-org.asynchttpclient.userAgent=AHC/2.0
+org.asynchttpclient.userAgent=AHC/2.1
 org.asynchttpclient.enabledProtocols=TLSv1.2, TLSv1.1, TLSv1
 org.asynchttpclient.enabledCipherSuites=TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_256_CBC_SHA
 org.asynchttpclient.useProxySelector=false

client/src/test/java/org/asynchttpclient/AsyncHttpClientDefaultsTest.java

@@ -76,7 +76,7 @@ public void testDefaultCompressionEnforced() {
     }
 
     public void testDefaultUserAgent() {
-        Assert.assertEquals(AsyncHttpClientConfigDefaults.defaultUserAgent(), "AHC/2.0");
+        Assert.assertEquals(AsyncHttpClientConfigDefaults.defaultUserAgent(), "AHC/2.1");
         testStringSystemProperty("userAgent", "defaultUserAgent", "MyAHC");
     }