Remove JCenter usages, fix import, and cleanup build.gradle file.

build.gradle

@@ -1,28 +1,18 @@
-subprojects {
-  repositories {
-    mavenCentral()
-  }
-}
-allprojects {
-    repositories {
-        mavenCentral()
-        jcenter()
-        maven {
-            url "https://maven.google.com"
-        }
-    }
-}
+
 buildscript {
     repositories {
-        mavenCentral()
-        maven {
-            url 'https://maven.google.com/'
-            name 'Google'
-        }
         google()
-        jcenter()
+        mavenCentral()
+        maven { url 'https://plugins.gradle.org/m2/' }
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:4.1.2'
     }
 }
+
+allprojects {
+    repositories {
+        mavenCentral()
+        maven { url 'https://plugins.gradle.org/m2/' }
+    }
+}

graphenej/build.gradle

@@ -10,17 +10,9 @@ android {
         versionName "0.6.0"
         vectorDrawables.useSupportLibrary = true
     }
-    buildTypes {
-        debug{}
-        preRelease{}
-        release {
-            minifyEnabled false
-            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
-        }
-    }
+
     defaultConfig {
         multiDexEnabled true
-        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
     }
 }
 

graphenej/src/androidTest/java/cy/agorise/graphenej/NodeLatencyVerifierTest.java

@@ -1,8 +1,9 @@
 package cy.agorise.graphenej;
 
-import android.support.test.runner.AndroidJUnit4;
 import android.util.Log;
 
+import androidx.test.runner.AndroidJUnit4;
+
 import org.junit.Test;
 import org.junit.runner.RunWith;