CI: Drop separate indexed_gzip test

Author: effigies

.travis.yml

@@ -13,8 +13,7 @@ cache:
     - $HOME/.cache/pip
 env:
     global:
-        - DEPENDS="six numpy scipy matplotlib h5py pillow pydicom"
-        - OPTIONAL_DEPENDS=""
+        - DEPENDS="six numpy scipy matplotlib h5py pillow pydicom indexed_gzip"
         - INSTALL_TYPE="setup"
         - CHECK_TYPE="test"
         - EXTRA_WHEELS="https://5cf40426d9f06eb7461d-6fe47d9331aba7cd62fc36c7196769e4.ssl.cf2.rackcdn.com"
@@ -74,10 +73,7 @@ matrix:
     - python: 3.5
       env:
         - CHECK_TYPE="doc_doctests"
-    # Run tests with indexed_gzip present
-    - python: 3.5
-      env:
-        - OPTIONAL_DEPENDS="indexed_gzip"
+
 before_install:
     - travis_retry python -m pip install --upgrade pip
     - travis_retry pip install --upgrade virtualenv
@@ -92,7 +88,8 @@ before_install:
     - if [ "${CHECK_TYPE}" == "style" ]; then
       travis_retry pip install flake8;
       fi
-    - travis_retry pip install $EXTRA_PIP_FLAGS $DEPENDS $OPTIONAL_DEPENDS
+    - travis_retry pip install $EXTRA_PIP_FLAGS $DEPENDS
+
 # command to install dependencies
 install:
     - |