BUG: requirements-dev: Could not find ... pyqt

As of today 'pyqt' is not a valid PyPI project.

This results in the error message

    Could not find a version that satisfies the requirement pyqt

when running

    python -m pip install -r requirements-dev.txt

from the contributors guide.

Author: jgehrcke

requirements-dev.txt

@@ -44,12 +44,12 @@ html5lib
 lxml
 openpyxl
 pyarrow>=0.9.0
-pyqt
+pyqt5
 tables>=3.4.2
 python-snappy
 s3fs
 sqlalchemy
 xarray
 xlrd
 xlsxwriter
-xlwt
+xlwt