update gradle wrapper and build tools

OpenKeychain/build.gradle

@@ -109,7 +109,6 @@ dependencies {
 
 android {
     compileSdkVersion rootProject.ext.compileSdkVersion
-    buildToolsVersion rootProject.ext.buildToolsVersion
 
     defaultConfig {
         minSdkVersion 15

build.gradle

@@ -6,7 +6,7 @@ buildscript {
 
     dependencies {
         // NOTE: Always use fixed version codes not dynamic ones, e.g. 0.7.3 instead of 0.7.+, see README for more information
-        classpath 'com.android.tools.build:gradle:3.1.4'
+        classpath 'com.android.tools.build:gradle:3.5.2'
         // bintray dependency to satisfy dependency of openpgp-api lib
         classpath 'com.novoda:bintray-release:0.8.0'
         classpath 'com.squareup.sqldelight:gradle-plugin:0.7.0'

extern/MaterialChipsInput/build.gradle

@@ -2,7 +2,6 @@ apply plugin: 'com.android.library'
 
 android {
     compileSdkVersion 27
-    buildToolsVersion "27.0.3"
 
     defaultConfig {
         minSdkVersion 15

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.9-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.0-all.zip

nfcsweetspot/build.gradle

@@ -5,7 +5,6 @@ dependencies {
 
 android {
     compileSdkVersion rootProject.ext.compileSdkVersion
-    buildToolsVersion rootProject.ext.buildToolsVersion
 
     defaultConfig {
         minSdkVersion 14