Update IntMap.java

STEPS and DOUBLE steps from 6 to 9:
0x0 	Stone Slab
0x1 	Sandstone Slab
0x2 	Wooden Slab
0x3 	Cobblestone Slab
0x4 	Brick Slab
0x5 	Stone Brick Slab
0x6 	Nether Brick Slab
0x7 	Quartz Slab
0x8 	Smooth Stone Slab (Double Only)
0x9 	Smooth Sandstone Slab (Double Only)