Travis CI: Do not update homebrew on macOS

Author: chfast

.travis.yml

@@ -62,9 +62,12 @@ cache:
         # Cache whole deps dir hoping you will not need to download and
         # build external dependencies next build.
         - $TRAVIS_BUILD_DIR/build/deps
-install:
-    - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then ./scripts/install_cmake.sh && ./scripts/install_solc_lllc.sh; fi
-    - ./scripts/install_deps.sh
+install: |
+    if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then
+      ./scripts/install_cmake.sh && ./scripts/install_solc_lllc.sh;
+    fi
+    export HOMEBREW_NO_AUTO_UPDATE=1
+    ./scripts/install_deps.sh
 before_script:
     - ./scripts/prepare_ccache.sh
     - travis_wait 150 ./scripts/build.sh $TRAVIS_BUILD_TYPE