build-unit-test-docker: Update CLI11 1.6.1 -> 1.7.1

Change-Id: I9abc8c3e492e7d771dde43c434a923f61dfd30aa
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/build-unit-test-docker.sh b/build-unit-test-docker.sh
index 37d3a3e..9a1142e 100755
--- a/build-unit-test-docker.sh
+++ b/build-unit-test-docker.sh
@@ -90,7 +90,7 @@
 declare -A PKG_REV=(
   [boost]=1.68.0
   [cereal]=v1.2.2
-  [CLI11]=v1.6.1
+  [CLI11]=v1.7.1
   # Snapshot from 2018-12-17
   [googletest]=9ab640ce5e5120021c5972d7e60f258bfca64d71
   [json]=v3.3.0