DOC/CI: ensure correct pandas version (GH15311) (#15317)

Author: jorisvandenbossche

ci/build_docs.sh

@@ -22,8 +22,8 @@ if [ x"$DOC_BUILD" != x"" ]; then
     echo "Will build docs"
 
     source activate pandas
-    conda install -n pandas -c r r rpy2 --yes
 
+    # install sudo deps
     time sudo apt-get $APT_ARGS install dvipng texlive-latex-base texlive-latex-extra
 
     mv "$TRAVIS_BUILD_DIR"/doc /tmp

ci/requirements-3.5_DOC_BUILD.sh

@@ -2,6 +2,8 @@
 
 source activate pandas
 
-echo "install DOC_BUILD"
+echo "[install DOC_BUILD deps]"
 
 conda install -n pandas -c conda-forge feather-format
+
+conda install -n pandas -c r r rpy2 --yes