include Mill plugin in Docker build

Author: lostiniceland

Dockerfile

@@ -13,6 +13,7 @@ COPY ./google_checkstyle.xml ${GEN_DIR}
 # All poms are copied, then we go offline, to allow for better caching of code changes without fetching all dependencies each time
 COPY ./modules/openapi-generator-gradle-plugin/pom.xml ${GEN_DIR}/modules/openapi-generator-gradle-plugin/
 COPY ./modules/openapi-generator-maven-plugin/pom.xml ${GEN_DIR}/modules/openapi-generator-maven-plugin/
+COPY ./modules/openapi-generator-mill-plugin/pom.xml ${GEN_DIR}/modules/openapi-generator-mill-plugin/
 COPY ./modules/openapi-generator-online/pom.xml ${GEN_DIR}/modules/openapi-generator-online/
 COPY ./modules/openapi-generator-cli/pom.xml ${GEN_DIR}/modules/openapi-generator-cli/
 COPY ./modules/openapi-generator-core/pom.xml ${GEN_DIR}/modules/openapi-generator-core/
@@ -23,6 +24,7 @@ RUN mvn dependency:go-offline
 # Modules are copied individually here to allow for caching of docker layers between major.minor versions
 COPY ./modules/openapi-generator-gradle-plugin ${GEN_DIR}/modules/openapi-generator-gradle-plugin
 COPY ./modules/openapi-generator-maven-plugin ${GEN_DIR}/modules/openapi-generator-maven-plugin
+COPY ./modules/openapi-generator-mill-plugin ${GEN_DIR}/modules/openapi-generator-mill-plugin
 COPY ./modules/openapi-generator-online ${GEN_DIR}/modules/openapi-generator-online
 COPY ./modules/openapi-generator-cli ${GEN_DIR}/modules/openapi-generator-cli
 COPY ./modules/openapi-generator-core ${GEN_DIR}/modules/openapi-generator-core