lower default insert size for bowtie2
lower default insert size for bowtie2

- although insert size can be changed as an arg to the script, the
  default should be set to handle typical Illumina data
- this is helpful for someone running the script without knowing about
  this setting

dpastling/cnv_pipeline,dpastling/plethora,dpastling/cnv_pipeline,dpastling/plethora,dpastling/plethora