Fix apt-get command in dockerfile

dockerfile

@@ -7,7 +7,7 @@
 # do not have to be installed every time the tests are run
 FROM debian:10
 RUN apt-get update --quiet && \
-    apt-get install --assume-yes --quiet --no-install-recommends && \
+    apt-get install --assume-yes --quiet --no-install-recommends \
         git cmake make gcc g++ gfortran \
         pocl-opencl-icd ocl-icd-opencl-dev opencl-clhpp-headers \
         python3-pyopencl python3-dev \