fix: use the correct agent (not slave)

Dockerfile

@@ -21,10 +21,9 @@
 #  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 #  THE SOFTWARE.
 
-#FROM adoptopenjdk/openjdk11:alpine
-FROM alpine:latest
+FROM alpine:3.13
 
-RUN apk add --no-cache openjdk11-jre-headless
+RUN apk add --no-cache openjdk11-jre-headless tini
 
 ARG VERSION=4.6
 ARG user=jenkins
@@ -44,6 +43,11 @@ RUN apk add --update --no-cache curl bash git git-lfs openssh-client openssl pro
   && chmod 644 /usr/share/jenkins/agent.jar \
   && ln -sf /usr/share/jenkins/agent.jar /usr/share/jenkins/slave.jar \
   && apk del curl
+
+COPY jenkins-agent /usr/local/bin/jenkins-agent
+RUN chmod +x /usr/local/bin/jenkins-agent &&\
+    ln -s /usr/local/bin/jenkins-agent /usr/local/bin/jenkins-slave
+
 USER ${user}
 ENV AGENT_WORKDIR=${AGENT_WORKDIR}
 RUN mkdir /home/${user}/.jenkins && mkdir -p ${AGENT_WORKDIR}
@@ -51,3 +55,5 @@ RUN mkdir /home/${user}/.jenkins && mkdir -p ${AGENT_WORKDIR}
 VOLUME /home/${user}/.jenkins
 VOLUME ${AGENT_WORKDIR}
 WORKDIR /home/${user}
+
+ENTRYPOINT ["/sbin/tini", "--", "/usr/local/bin/jenkins-agent"]