[C+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**
Fixing a failing test caused by an api change

**PR Breakdown**
Fix the [failing unit test](https://github.com/Bukkit/CraftBukkit/blob/master/src/test/java/org/bukkit/PerMaterialTest.java#L141) affected by the bukkit PR

**Testing Results and Materials**
[Source](https://gist.github.com/8453276) - [Plugin](https://www.dropbox.com/s/reeuhjeg0s9rzgf/TestPlugin-1.0.jar)

**JIRA Ticket**
https://bukkit.atlassian.net/browse/BUKKIT-5255

**Associated Bukkit PR**
[Link](https://github.com/Bukkit/Bukkit/pull/1006)