added proguard rules

now they are part of the .aar library, before you had to add them to each release app

usbSerialForAndroid/build.gradle

@@ -7,19 +7,14 @@ android {
     defaultConfig {
         minSdkVersion 17
         targetSdkVersion 28
+        consumerProguardFiles 'proguard-rules.pro'
+        
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
         testInstrumentationRunnerArguments = [                    // Raspi   Windows   LinuxVM   ...
                 'rfc2217_server_host': '192.168.0.100',
                 'rfc2217_server_nonstandard_baudrates': 'true',   // true    false     false
         ]
     }
-
-    buildTypes {
-        release {
-            minifyEnabled false
-            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
-        }
-    }
 }
 
 dependencies {