Update base version in documentation.

Florian Loretan · web-flow · commit 4adc47b597bf · 2019-06-26T17:07:25.000+02:00
diff --git a/README.md b/README.md
@@ -1,5 +1,5 @@
 # silta-circleci
-A docker image used circleCI, based on `circleci/php:7.1-node-browser` with the following additions:
+A docker image used circleCI, based on `circleci/php:7.3-cli-node` with the following additions:
 
 - Composer configured correctly
 - Drush-launcher, prestissimo and coder pre-installed
