Update Yarn to version 1.5.1 (#6689)

Dockerfile

@@ -9,8 +9,8 @@ ARG GID=991
 ENV RAILS_SERVE_STATIC_FILES=true \
     RAILS_ENV=production NODE_ENV=production
 
-ARG YARN_VERSION=1.3.2
-ARG YARN_DOWNLOAD_SHA256=6cfe82e530ef0837212f13e45c1565ba53f5199eec2527b85ecbcd88bf26821d
+ARG YARN_VERSION=1.5.1
+ARG YARN_DOWNLOAD_SHA256=cd31657232cf48d57fdbff55f38bfa058d2fb4950450bd34af72dac796af4de1
 ARG LIBICONV_VERSION=1.15
 ARG LIBICONV_DOWNLOAD_SHA256=ccf536620a45458d26ba83887a983b96827001e92a13847b45e4925cc8913178