Update Hugo to version 0.81.0

Dockerfile

@@ -9,9 +9,9 @@
 # to work around segmentation fault issues.
 FROM golang:1.13-alpine
 ARG HUGO=hugo
-ARG HUGO_VERSION=0.80.0
-ARG HUGO_SHA=b3a259bbe633e2f9182f8ecfc1b5cee6a7cfc4c970defe5f29c9959f2ef3259b
-ARG HUGO_EXTENDED_SHA=8405248a7234af657979a209d6778afaabd9b40857b7274649ee952ce2937bed
+ARG HUGO_VERSION=0.81.0
+ARG HUGO_SHA=35099b33780075ed9c709296f371d6b9fd44fa9ed3d26af4266ed6be4097250d
+ARG HUGO_EXTENDED_SHA=3c7d034405c67bf571b6d8f001d5a9c49dd87dbfa32b3b19d16e898c46f8f5e2
 RUN set -eux && \
     case ${HUGO} in \
       *_extended) \