Update Dockerfile

Dockerfile

@@ -33,7 +33,7 @@ RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-ins
         rm -rf /var/lib/apt/lists/*
 
 RUN git clone https://github.com/lee-ny/teaching_arithmetic.git /teaching_arithmetic
-RUN chmod+x /teaching_arithmetic
+RUN chmod +x /teaching_arithmetic
 # Install conda
 # translating Docker's TARGETPLATFORM into mamba arches
 RUN case ${TARGETPLATFORM} in \