feat: update apcu version to 5.1.20 (#140)

Author: torbenbr

Dockerfile

@@ -25,7 +25,7 @@ RUN apk add --no-cache \
 # see https://github.com/docker-library/php/issues/240#issuecomment-763112749
 ENV LD_PRELOAD /usr/lib/preloadable_libiconv.so
 
-ARG APCU_VERSION=5.1.19
+ARG APCU_VERSION=5.1.20
 RUN set -eux; \
 	apk add --no-cache --virtual .build-deps \
 		$PHPIZE_DEPS \