fix: use yarn to install expo cli globally

This is related to NPM failing for both iltorb and sharp dependencies. Let's work around this by using Yarn for now.

expo/expo-cli#591

base/Dockerfile

@@ -5,9 +5,8 @@ LABEL repository="https://github.com/expo/expo-github-action"
 LABEL homepage="https://github.com/expo/expo-github-action/blob/master/base"
 LABEL maintainer="Cedric van Putten <[email protected]>"
 
-RUN npm install --global expo-cli@2 \
-	&& npm cache rm --force \
-	&& rm -rf ~/.npm
+RUN yarn global add expo-cli@2 \
+	&& yarn cache clean
 
 COPY entrypoint.sh LICENSE.md README.md /