CH34x flow control

the tests look like the CH34x only partially supports flow control
CTS ok: writing data correctly blocks if CTS is unset.
RTS not ok: when not reading data (fast enough), RTS is not unset on buffer full

usbSerialForAndroid/build.gradle

@@ -54,7 +54,7 @@ project.afterEvaluate {
                 // values used for local maven repo, jitpack uses github release:
                 groupId 'com.github.mik3y'
                 artifactId 'usb-serial-for-android'
-                version '3.9.1beta'
+                version '3.12.0beta'
             }
         }
     }