fix option for RUST_CONFIGURE_ARGS to be rust.ignore-git=false

Author: JeremySorensen

Diff for: src/ci/docker/x86_64-gnu-distcheck/Dockerfile

@@ -18,6 +18,6 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
-ENV RUST_CONFIGURE_ARGS --build=x86_64-unknown-linux-gnu --set build.ignore-git=false
+ENV RUST_CONFIGURE_ARGS --build=x86_64-unknown-linux-gnu --set rust.ignore-git=false
 ENV SCRIPT python2.7 ../x.py test distcheck
 ENV DIST_SRC 1