Remove miniconda installer caching (scikit-learn#8859)

Download takes less than a second both on Travis and Circle.

Also use latest miniconda installer on Circle.

.travis.yml

@@ -8,7 +8,6 @@ cache:
   apt: true
   directories:
   - $HOME/.cache/pip
-  - $HOME/download
 addons:
   apt:
     packages:

build_tools/circle/build_doc.sh

@@ -96,22 +96,11 @@ if [[ `type -t deactivate` ]]; then
 fi
 
 # Install dependencies with miniconda
-pushd .
-cd
-mkdir -p download
-cd download
-echo "Cached in $HOME/download :"
-ls -l
-if [[ ! -f miniconda.sh ]]
-then
-   wget https://repo.continuum.io/miniconda/Miniconda-latest-Linux-x86_64.sh \
+wget https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh \
    -O miniconda.sh
-fi
 chmod +x miniconda.sh && ./miniconda.sh -b -p $MINICONDA_PATH
-cd ..
 export PATH="$MINICONDA_PATH/bin:$PATH"
 conda update --yes --quiet conda
-popd
 
 # Configure the conda environment and put it in the path using the
 # provided versions

build_tools/travis/install.sh

@@ -28,22 +28,13 @@ if [[ "$DISTRIB" == "conda" ]]; then
     # conda-based environment instead
     deactivate
 
-    # Use the miniconda installer for faster download / install of conda
-    # itself
-    pushd .
-    cd
-    mkdir -p download
-    cd download
-    echo "Cached in $HOME/download :"
-    ls -l
-    echo
+    # Install miniconda
     wget https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh \
         -O miniconda.sh
-    chmod +x miniconda.sh && ./miniconda.sh -b -p /home/travis/miniconda
-    cd ..
-    export PATH=/home/travis/miniconda/bin:$PATH
+    MINICONDA_PATH=/home/travis/miniconda
+    chmod +x miniconda.sh && ./miniconda.sh -b -p $MINICONDA_PATH
+    export PATH=$MINICONDA_PATH/bin:$PATH
     conda update --yes conda
-    popd
 
     # Configure the conda environment and put it in the path using the
     # provided versions

circle.yml

@@ -11,7 +11,6 @@ dependencies:
   cache_directories:
     - "~/scikit_learn_data"
     - "~/scikit-learn.github.io"
-    - "~/download"
   # Check whether the doc build is required, install build dependencies and
   # run sphinx to build the doc.
   override: