visualizations.sh: use cp;rm instead of mv in /tmp

mktemp creates a file with mode 0600 and group wheel (inherited from
/tmp/). The command mv is then not able to set group ownership to wheel
in /var/db/builder-web/ on FreeBSD and emits a warning. Furthermore, the
restrictive permissions are preserved. Copying and then removing the
temporary file avoids these issues.

packaging/visualizations.sh

@@ -155,7 +155,8 @@ if [ -e "${DEPENDENCIES_VIZ_FILENAME}" ]; then
     info "Dependency visualization already exists: '${DEPENDENCIES_VIZ_FILENAME}'"
 else
     if ${OPAM_GRAPH} --output-format=html "${OPAM_SWITCH}" > "${TMPDEPENDENCIES}"; then
-        mv "${TMPDEPENDENCIES}" "${DEPENDENCIES_VIZ_FILENAME}"
+        cp "${TMPDEPENDENCIES}" "${DEPENDENCIES_VIZ_FILENAME}"
+        rm "$TMPDEPENDENCIES"
     else
         die "opam-graph failed to generate visualization"
     fi
@@ -201,7 +202,8 @@ if [ -n "${DEBUG_BIN_RELATIVE}" ]; then
                 "${DEBUG_BIN}" \
                 > "${TMPTREE}"
         then
-            mv "${TMPTREE}" "${TREEMAP_VIZ_FILENAME}"
+            cp "${TMPTREE}" "${TREEMAP_VIZ_FILENAME}"
+            rm "$TMPTREE"
         else
             die "modulectomy failed to generate visualization"
         fi