removed maptools in DESCRIPTION

maptools is not used for CALDER2

DESCRIPTION

@@ -32,7 +32,6 @@ Imports:
 	Matrix (>= 1.2.17),
 	rARPACK (>= 0.11.0),
 	factoextra (>= 1.0.5),
-	maptools (>= 0.9.5),
 	data.table (>= 1.12.2),
 	fields (>= 9.8.3),
 	GenomicRanges (>= 1.36.0),