presentation branch's rest build.gradle denpencies updates -downgrade jackson-databind-2.9.0 to 2.8.7

[mingqin1]

Hi:
The current build.gradle will import jackson-databind-2.9.0 jar which causes springboot's staring up failure for reason of java.lang.NoClassDefFoundError: com/fasterxml/jackson/annotation/JsonMerge.

After modifying the build.gradle's dependencies as following , spring boot starts up successfully.

dependencies {
compile ".............
..............
"javax.servlet:jstl"
compile "com.fasterxml.jackson.core:jackson-databind:2.8.7"
compile ('com.maxmind.geoip2:geoip2:2.7.0'){
exclude group: 'com.fasterxml.jackson.core', module: 'jackson-databind'
}

Another way to learn:
The netbeans 8.2 tested maven version of presentation branch is post here -https://github.com/mingqin1/spring-security-4.1-and-beyond/tree/presentation . The maven converted codes serve the purpose of encourage of learning . All the credits go to Rob Winch, Joe Grandja