Update hello_material.adoc

Modified the column width of the Default Material Definitions table to take advantage of extra space gained by removing duplicate word Common from cell 1.

src/docs/asciidoc/jme3/beginner/hello_material.adoc

@@ -308,7 +308,7 @@ To deactivate Shininess, do not set `Shininess` to 0, but instead set the `Specu
 == Default Material Definitions
 
 As you have seen, you can find the following default materials in `jme/core-data/Common/…`.
-[cols="3", options="header"]
+[cols="30,35,35", options="header"]
 |===
 
 a| Default Definition