Add 'Automatic-Module-Name' property to aws-lambda-java-core MANIFEST.MF

`aws-lambda-java-core`'s lack of an `Automatic-Module-Name` property in its `META-INF/MANIFEST.MF` is preventing me from modularizing my Java project.

Attempting to require the automatic module in my `module-info.java` with
`requires aws.lambda.java.core;` results in the following Gradle error:

> Task :*******:compileJava FAILED
C:\Users\Jacob\IdeaProjects\***-******-*********\*******\src\main\java\module-info.java:4: error: module not found: aws.lambda.java.core
requires aws.lambda.java.core;

Environment:

```
C:\Users\Jacob\IdeaProjects\***-******-*********>gradlew -v

------------------------------------------------------------
Gradle 6.5
------------------------------------------------------------

Build time: 2020-06-02 20:46:21 UTC
Revision: a27f41e4ae5e8a41ab9b19f8dd6d86d7b384dad4

Kotlin: 1.3.72
Groovy: 2.5.11
Ant: Apache Ant(TM) version 1.10.7 compiled on September 1 2019
JVM: 14.0.1 (Oracle Corporation 14.0.1+7)
OS: Windows 10 10.0 amd64
```