Fix build_index method to default threads to 0 instead of 2 for better control

Author: kojix2

lib/hts/bam.rb

@@ -93,10 +93,10 @@ def initialize(file_name, mode = "r", index: nil, fai: nil, threads: nil,
       @start_position = tell
     end
 
-    def build_index(index_name = nil, min_shift: 0, threads: 2, verbose: true)
+    def build_index(index_name = nil, min_shift: 0, verbose: true)
       check_closed
 
-      self.class.build_index(@file_name, index_name, min_shift, @nthreads || threads, verbose)
+      self.class.build_index(@file_name, index_name, min_shift, @nthreads || 0, verbose)
       self # for method chaining
     end