[B] Material.DRAGON_EGG.hasGravity should return true. Fixes BUKKIT-5255

**The issue**
The Material.DRAGON_EGG.hasGravity() method currently returns false but should return true. See [wiki](http://minecraft.gamepedia.com/Dragon_Egg#Behavior).

**Justification for this PR**
Does it really need one?

**PR Breakdown**
Add the dragon egg to the list of blocks having gravity

**Testing Results and Materials**
```java
getLogger().info(Material.DRAGON_EGG.hasGravity() ? "true" : "false");
```

**JIRA Ticket**
https://bukkit.atlassian.net/browse/BUKKIT-5255