0.5.0 upgrade instructions do not mention removal of inmemory backend from janusgraph-core

[FieteO]

While upgrading from Janusgraph 0.4.1 to 0.5.0 I noticed that my test cases that use the inmemory backend started to fail with a ClassNotFoundException for the InMemoryStoreManager. I then looked at the Upgrade Instructions for 0.5.0 and couldn't find any mention of the inmemory backend. Upon investigating in the code, I saw that the class was moved into a newly created janusgraph-inmemory module.

I am sure other users can do that too, but I think this change should be mentioned in the upgrade instructions. In particular, that for users that use the inmemory backend, it's necessary to add the janusgraph-inmemory dependency:

<dependency>
    <groupId>org.janusgraph</groupId>
    <artifactId>janusgraph-inmemory</artifactId>
    <scope>test</scope>
    <version>0.5.0</version>
</dependency>