Fix for cljam level command

[ayamada]

cljam level command needs index from internal bam reader, but bam reader without option args means :ignore-index true.
Need exipit :ignore-index false option.

[codecov-io]

Codecov Report

Merging #57 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master      #57   +/-   ##
=======================================
  Coverage   73.36%   73.36%           
=======================================
  Files          56       56           
  Lines        3293     3293           
  Branches      329      329           
=======================================
  Hits         2416     2416           
  Misses        548      548           
  Partials      329      329

Impacted Files	Coverage Δ
src/cljam/cli.clj	33.59% <0%> (ø)	⬆️

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