[ci] Fix Travis macOS bot ICU issue (#1472)

.travis.yml

@@ -51,8 +51,10 @@ matrix:
         - brew update;
           # Workaround Travis/brew bug
         - brew uninstall libtool && brew install libtool
-        - brew install ragel freetype glib gobject-introspection cairo icu4c graphite2 || true
-        - brew link --force icu4c # icu4c is keg-only
+        - brew install ragel freetype glib gobject-introspection cairo graphite2 || true
+        - brew upgrade icu4c || true
+        - export PATH="/usr/local/opt/icu4c/sbin:/usr/local/opt/icu4c/bin:$PATH"
+        - export PKG_CONFIG_PATH="/usr/local/opt/icu4c/lib/pkgconfig"
       script:
         - ./autogen.sh
         - ./configure $CONFIGURE_OPTS --with-coretext