🐛 fix syntax error

[chfw]

With your PR, here is a check list:

• Has test cases written?
• Has all code lines tested?
• Has make format been run?
• Please update CHANGELOG.yml(not CHANGELOG.rst)
• Has fair amount of documentation if your change is complex
• Agree on NEW BSD License for your contribution

[codecov-commenter]

Codecov Report

Merging #51 (ad4aa68) into master (7fe8861) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #51   +/-   ##
=======================================
  Coverage   97.89%   97.89%           
=======================================
  Files          13       13           
  Lines         711      711           
=======================================
  Hits          696      696           
  Misses         15       15           

Impacted Files	Coverage Δ
pyexcel_xls/xlsr.py	98.49% <ø> (ø)
pyexcel_xls/xlsw.py	98.30% <ø> (ø)

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