Require Emscripten 2.0.18
Require Emscripten 2.0.18

Change-Id: I04fe7041fcd82d08416c37a6e95c36acb70c39dc

PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp