Dockerfile: dumb fix

Author: chathhorn

Dockerfile

@@ -59,7 +59,7 @@ RUN cd ${DEPS_DIR}/k/llvm-backend/src/main/native \
 # Build K. #
 ############
 
-RUN source /home/user/.cargo/env \
+RUN . /home/user/.cargo/env \
   && cd ${DEPS_DIR}/k \
   && mvn package -e -q -U \
       -DskipTests -DskipKTest \