Fix decompiling GPKG on 64bit systems

array.array("L") reads 64bit ints, not 32bit.  Use "I" instead.
diff --git a/Lib/fontTools/ttLib/tables/G_P_K_G_.py b/Lib/fontTools/ttLib/tables/G_P_K_G_.py
index 46175f5..8ffd2d6 100644
--- a/Lib/fontTools/ttLib/tables/G_P_K_G_.py
+++ b/Lib/fontTools/ttLib/tables/G_P_K_G_.py
@@ -23,7 +23,7 @@
 	def decompile(self, data, ttFont):
 		dummy, newData = sstruct.unpack2(GPKGFormat, data, self)
 
-		GMAPoffsets = array.array("L")
+		GMAPoffsets = array.array("I")
 		endPos = (self.numGMAPs+1) * 4
 		GMAPoffsets.fromstring(newData[:endPos])
 		if sys.byteorder <> "big":
@@ -35,7 +35,7 @@
 			self.GMAPs.append(data[start:end])
 		pos = endPos
 		endPos = pos + (self.numGlyplets + 1)*4
-		glyphletOffsets = array.array("L")
+		glyphletOffsets = array.array("I")
 		glyphletOffsets.fromstring(newData[pos:endPos])
 		if sys.byteorder <> "big":
 			glyphletOffsets.byteswap()