[ci] Sort out Travis configuration

Use a matrix to avoid a gazillion if's.
diff --git a/.ci/deploy-docs.sh b/.ci/deploy-docs.sh
index 086982b..a8a8523 100755
--- a/.ci/deploy-docs.sh
+++ b/.ci/deploy-docs.sh
@@ -3,6 +3,8 @@
 set -x
 set -o errexit -o nounset
 
+if test "x$TRAVIS_SECURE_ENV_VARS" != xtrue; then exit; fi
+
 BRANCH="$TRAVIS_BRANCH"
 if test "x$BRANCH" != xmaster; then exit; fi