remove a line break

apparently we need to clean the line break
$ ./build/bin/sage-get-system-packages debian _bootstrap _prereq
autoconf automake libtool
binutils make m4 perl flex python3 tar bc gcc libbz2-dev bzip2 g++ ca-certificates patch pkg-config libz-dev

Author: dimpase

docker/Dockerfile

@@ -90,7 +90,7 @@ RUN ln -s /usr/bin/sage /usr/bin/sagemath
 # We need gcc/g++ and libstdc++-10-dev to allow compilation of cython at run-time from the notebook.
 # We also install sudo for the sage user, see below.
 RUN apt-get -qq update \
-    && apt-get -qq install -y --no-install-recommends gfortran gcc g++ libstdc++-10-dev sudo openssl $(build/bin/sage-get-system-packages debian _bootstrap _prereq)\
+    && apt-get -qq install -y --no-install-recommends gfortran gcc g++ libstdc++-10-dev sudo openssl $(echo $(build/bin/sage-get-system-packages debian _bootstrap _prereq))\
     && apt-get -qq clean \
     && rm -r /var/lib/apt/lists/*
 # Sage refuses to build as root, so we add a "sage" user that can sudo without a password.