Fix inconsistent path of sfs folder

The path of sfs folder is defined by user in names_and_entities.pig.params. But "./sfs" is used as the path of sfs folder here,which may cause the following error:


java.lang.NullPointerException
	at pignlproc.helpers.RestrictedNGramGenerator.exec(RestrictedNGramGenerator.java:98)
	at pignlproc.helpers.RestrictedNGramGenerator.exec(RestrictedNGramGenerator.java:44)
	at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNext(POUserFunc.java:337)
	at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNext(POUserFunc.java:381)