DOC: change doc build to python 3.6 (#16545)

* DOC: change doc build to python 3.6

* Remove pinning of pyqt to 4.x

* Remove pinning of openpyxl

* Add xsel to doc build for clipboard

Author: jorisvandenbossche

.travis.yml

@@ -74,7 +74,11 @@ matrix:
     # In allow_failures
     - os: linux
       env:
-        - JOB="3.5_DOC" DOC=true
+        - JOB="3.6_DOC" DOC=true
+      addons:
+        apt:
+          packages:
+          - xsel
     allow_failures:
       - os: linux
         env:
@@ -87,7 +91,7 @@ matrix:
           - JOB="3.6_NUMPY_DEV" TEST_ARGS="--skip-slow --skip-network" PANDAS_TESTING_MODE="deprecate"
       - os: linux
         env:
-          - JOB="3.5_DOC" DOC=true
+          - JOB="3.6_DOC" DOC=true
 
 before_install:
   - echo "before_install"

ci/requirements-3.5_DOC.build renamed to ci/requirements-3.6_DOC.build

@@ -1,4 +1,4 @@
-python=3.5*
+python=3.6*
 python-dateutil
 pytz
 numpy

ci/requirements-3.5_DOC.run renamed to ci/requirements-3.6_DOC.run

@@ -12,7 +12,7 @@ lxml
 beautifulsoup4
 html5lib
 pytables
-openpyxl=1.8.5
+openpyxl
 xlrd
 xlwt
 xlsxwriter
@@ -21,4 +21,4 @@ numexpr
 bottleneck
 statsmodels
 xarray
-pyqt=4.11.4
+pyqt