Fix description

[mremes]

Big Query -> BigQuery

[codecov-io]

Codecov Report

Merging #130 into master will decrease coverage by 44.71%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #130       +/-   ##
===========================================
- Coverage    75.7%   30.99%   -44.72%     
===========================================
  Files           8        8               
  Lines        1626     1626               
===========================================
- Hits         1231      504      -727     
- Misses        395     1122      +727

Impacted Files	Coverage Δ
pandas_gbq/tests/test_gbq.py	26.88% <0%> (-56.76%)	⬇️
pandas_gbq/gbq.py	20.56% <0%> (-55.8%)	⬇️
pandas_gbq/_load.py	62.5% <0%> (-35%)	⬇️

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[parthea]

Thanks!