Update to ergo 2.15+

docker/test/alpine/Dockerfile

@@ -1,13 +1,17 @@
 # This Dockerfile creates a docker image suitable to run biboumi’s build and
 # tests.  For example, it can be used on with gitlab-ci.
 
-FROM alpine:latest
+FROM docker.io/alpine:edge
 
 ENV LC_ALL C.UTF-8
 
+# py3-slixmpp is in testing repo
+RUN echo "https://dl-cdn.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories
+
 # Needed to build biboumi
 RUN apk add --no-cache \
 git \
+ergo \
 make \
 cmake \
 g++ \
@@ -24,6 +28,7 @@ catch2-3 \
 valgrind \
 py3-pip \
 py3-lxml \
+py3-slixmpp \
 python3-dev \
 libffi-dev \
 go \
@@ -31,8 +36,3 @@ rust \
 cargo \
 wget
 
-# Install oragono, for e2e tests
-RUN wget "https://github.com/ergochat/ergo/archive/v2.0.0.tar.gz" && tar xvf "v2.0.0.tar.gz" && cd "ergo-2.0.0" && make && cp ~/go/bin/oragono /usr/local/bin/oragono
-
-# Install slixmpp, for e2e tests
-RUN pip3 install slixmpp --break-system-packages