Put if statement dockerfile over multiple lines

Author: mcbarton

ci/docker/Dockerfile

@@ -29,9 +29,13 @@ RUN ARCH=$(uname -m) \
 ENV PATH /opt/cmake/bin:$PATH
 
 # As with CMake install a later version of Ninja than waht 18.04 has.
-# FIXME as part of PR. Write if statement over multiple lines
 RUN ARCH=$(uname -m) \
-  && if [ "$ARCH" = "aarch64"  ]; then curl -sSLO https://github.com/ninja-build/ninja/releases/download/v1.12.1/ninja-linux-aarch64.zip ; unzip ninja-linux-aarch64.zip; else curl -sSLO https://github.com/ninja-build/ninja/releases/download/v1.12.1/ninja-linux.zip ; unzip ninja-linux.zip; fi \
+  && if [ "$ARCH" = "aarch64"  ]; then \
+  &&   curl -sSLO https://github.com/ninja-build/ninja/releases/download/v1.12.1/ninja-linux-aarch64.zip ; \
+  && else \
+  &&   curl -sSLO https://github.com/ninja-build/ninja/releases/download/v1.12.1/ninja-linux.zip ; 
+  && fi \
+  && unzip ninja*.zip \
   && rm *.zip \
   && mv ninja /opt/cmake/bin