signer dockerfile build with only published dependencies

dockerfiles/phone-number-privacy/Dockerfile

@@ -40,7 +40,7 @@ COPY .gitmodules .gitmodules
 # Setting ONLY_PUBLISHED_DEPENDENCIES to true or any non-empty string results in only the
 # phone-number-privacy package being copied into the image, and therefore it will only build using
 # published dependencies. Setting ONLY_PUBLISHED_DEPENDENCIES to "" will copy in all dependecies.
-ARG ONLY_PUBLISHED_DEPENDENCIES=""
+ARG ONLY_PUBLISHED_DEPENDENCIES="true"
 ARG PACKAGE_SELECTOR=${ONLY_PUBLISHED_DEPENDENCIES:+phone-number-privacy/signer}
 COPY --from=packages celo-phone-number-privacy/packages/${PACKAGE_SELECTOR} packages/${PACKAGE_SELECTOR}