builds_packages: Line wrap long DEFINE_boolean line.

This is followup from
https://crrev.com/c/2775837/1/build_packages#77

BUG=chromium:945003
TEST=./build_packages --board eve --skip_setup_board

Change-Id: Ied7a2e4db247c1ba229958c8775ccaed9d094433
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2817912
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Michael Mortensen <mmortensen@google.com>
diff --git a/build_packages b/build_packages
index 234d50f..beee931 100755
--- a/build_packages
+++ b/build_packages
@@ -74,7 +74,8 @@
 DEFINE_boolean skip_chroot_upgrade "${FLAGS_FALSE}" \
   "Don't run the chroot upgrade automatically; use with care."
 DEFINE_boolean skip_setup_board "${FLAGS_FALSE}" \
-  "Don't run setup_board. Implies skip_chroot_upgrade and skip_toolchain_update."
+  "Don't run setup_board. Implies skip_chroot_upgrade and" \
+  "skip_toolchain_update."
 DEFINE_boolean skip_toolchain_update "${FLAGS_FALSE}" \
   "Don't update toolchain automatically."
 DEFINE_boolean withdev "${FLAGS_TRUE}" \