Fix mermaid plugin installation.

Dockerfile

@@ -17,6 +17,8 @@ RUN curl -L --output redmine-${REDMINE_VERSION}.zip https://github.com/redmine/r
 
 WORKDIR /usr/src/redmine/plugins
 
+COPY redmine_checklists redmine_checklists
+
 RUN git clone https://github.com/kenkubomi/redmine_add_absolute_time.git && \
   cd redmine_add_absolute_time && \
   git reset --hard 8b8f79320f836fd05c942ed39b1b749a4418d18f && \
@@ -45,10 +47,9 @@ RUN git clone https://github.com/kenkubomi/redmine_add_absolute_time.git && \
   git reset --hard 3d71bdc6166b9ad9334e2cfa67de60d1c308a9b3 && \
   cd /usr/src/redmine/plugins && \
   git clone https://github.com/enricohuang/redmine_mermaid.git && \
+  cd redmine_mermaid && \
   git reset --hard 60c89454a1616b31bf73716d24d2e95a22a57eff
 
-COPY redmine_checklists redmine_checklists
-
 WORKDIR /usr/src/redmine/public/themes
 
 RUN curl -L --output v${OPALE_VERSION}.tar.gz https://github.com/gagnieray/opale/archive/refs/tags/${OPALE_VERSION}.tar.gz && \