Remove -Xbootlasspath/a option of the cljam executable

[alumi]

Fixes #295

This PR removes -Xbootclasspath/a option from the header of the cljam executable built by lein bin to avoid a NPE from commons-compress >= 1.21.
The default value of :bootclasspath in lein-binplus is false.

• When loading the class org.apache.commons.compress.utils.OsgiUtils, its static initializer calls getClassLoader but the return value will be null when the class is loaded by a bootstrap classloader.
• lein-binplus adds the -Xbootclasspath/a option when :bootclasspath is truthy
• So this can be fixed by removing :bootclasspath true in project.clj

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8cf394e) 88.31% compared to head (7e65858) 88.31%.
Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #296      +/-   ##
==========================================
- Coverage   88.31%   88.31%   -0.01%     
==========================================
  Files          81       83       +2     
  Lines        7058     7306     +248     
  Branches      488      492       +4     
==========================================
+ Hits         6233     6452     +219     
- Misses        337      366      +29     
  Partials      488      488              

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[alumi]

The issue will be solved by upgrading commons-compress to >= 1.25.1