[MapD] Fixed where operator - Fixes #1623

[xmnlab]

This PR fixes #1623

[xmnlab]

@cpcloud @kszucs

the conda build is failing for windows. do you have any idea about this error?

[cpcloud]

@xmnlab Yep, I've got #1660 up to address this.

[cpcloud]

@xmnlab Can you add a test here?

[xmnlab]

@cpcloud sure! I am working on that!

[codecov]

Codecov Report

Merging #1653 into master will decrease coverage by 2.63%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1653      +/-   ##
==========================================
- Coverage   89.91%   87.28%   -2.64%     
==========================================
  Files         185      185              
  Lines       27207    27218      +11     
  Branches     2337     2337              
==========================================
- Hits        24463    23757     -706     
- Misses       2340     3054     +714     
- Partials      404      407       +3

Impacted Files	Coverage Δ
ibis/mapd/operations.py	71.1% <100%> (+0.47%)	⬆️
ibis/mapd/tests/test_operations.py	95.23% <100%> (+1.9%)	⬆️
ibis/bigquery/tests/test_client.py	25.87% <0%> (-73.55%)	⬇️
ibis/bigquery/tests/test_compiler.py	39.89% <0%> (-60.11%)	⬇️
ibis/bigquery/udf/tests/test_udf_execute.py	28% <0%> (-54%)	⬇️
ibis/bigquery/client.py	42.91% <0%> (-52.37%)	⬇️
ibis/bigquery/compiler.py	58.82% <0%> (-38.61%)	⬇️
ibis/bigquery/tests/conftest.py	70.27% <0%> (-16.22%)	⬇️
ibis/bigquery/udf/api.py	80.48% <0%> (-14.64%)	⬇️
ibis/impala/compiler.py	91.04% <0%> (-5.75%)	⬇️
... and 10 more

[xmnlab]

it is ready for review!

[cpcloud]

LGTM. Thanks @xmnlab