BUGFIX: correct off-by-one error in BED output

The BED-formatted output was not correctly reverting
intron start coordinates to 0-based indexing as
required by the BED format spec. Thanks to @MichaelHiller for bringing
this to my attention.

intronIC/intronIC.py

@@ -4251,6 +4251,7 @@ def output_format(
             attribs.insert(1, rounded_score)
             attribs.insert(2, dnts)
     elif out_type == 'BED':
+        attribs[1] -= 1  # revert start to 0-based indexing
         attribs.insert(3, label)
     if separator is not None:
         attribs = separator.join([str(a) for a in attribs])