docker: executable file not found in $PATH

I have a docker image which installs grunt, but when I try to run it, I get an error:

Error response from daemon: Cannot start container foo_1: \
    exec: "grunt serve": executable file not found in $PATH

If I run bash in interactive mode, grunt is available.

What am I doing wrong?

Here is my Dockerfile:

# https://registry.hub.docker.com/u/dockerfile/nodejs/ (builds on ubuntu:14.04)
FROM dockerfile/nodejs

MAINTAINER My Name, me@email.com

ENV HOME /home/web
WORKDIR /home/web/site

RUN useradd web -d /home/web -s /bin/bash -m

RUN npm install -g grunt-cli
RUN npm install -g bower

RUN chown -R web:web /home/web
USER web

RUN git clone https://github.com/repo/site /home/web/site

RUN npm install
RUN bower install --config.interactive=false --allow-root

ENV NODE_ENV development

# Port 9000 for server
# Port 35729 for livereload
EXPOSE 9000 35729
CMD ["grunt"]