Update gradle to version 6.7

Use the Java Library plugin and switch to the new (non-deprecated)
syntax for declaring dependencies.
Various other cleanups/modernizations in build.gradle.

Change-Id: Iac6734562eeda68c588a93775596f1e598eafd1f
diff --git a/gradlew b/gradlew
index 2fe81a7..4f906e0 100755
--- a/gradlew
+++ b/gradlew
@@ -82,6 +82,7 @@
 
 CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
 
+
 # Determine the Java command to use to start the JVM.
 if [ -n "$JAVA_HOME" ] ; then
     if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
@@ -129,6 +130,7 @@
 if [ "$cygwin" = "true" -o "$msys" = "true" ] ; then
     APP_HOME=`cygpath --path --mixed "$APP_HOME"`
     CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+
     JAVACMD=`cygpath --unix "$JAVACMD"`
 
     # We build the pattern for arguments to be converted via cygpath