Revert to Android build-tools 26.0.0

since Travis CI doesn't seem to have a later version yet

Author: mannodermaus

sample/build.gradle

@@ -21,7 +21,7 @@ apply plugin: "de.mannodermaus.android-junit5"
 
 android {
     compileSdkVersion 26
-    buildToolsVersion "26.0.1"
+    buildToolsVersion "26.0.0"
 
     defaultConfig {
         applicationId "de.mannodermaus.gradle.plugins.android_junit5.sample"