Bump to 1.9.1-1~jessie

```console
$ curl -fsSL 'http://nginx.org/packages/mainline/debian/dists/jessie/nginx/binary-amd64/Packages' | awk -F ': ' '$1 == "Package" { pkg = $2 } pkg == "nginx" && $1 == "Version" { print $2 }' | sort -V | tail -1
```

Author: tianon

Dockerfile

@@ -5,7 +5,7 @@ MAINTAINER NGINX Docker Maintainers "[email protected]"
 RUN apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys 573BFD6B3D8FBC641079A6ABABF5BD827BD9BF62
 RUN echo "deb http://nginx.org/packages/mainline/debian/ jessie nginx" >> /etc/apt/sources.list
 
-ENV NGINX_VERSION 1.9.0-1~jessie
+ENV NGINX_VERSION 1.9.1-1~jessie
 
 RUN apt-get update && \
     apt-get install -y ca-certificates nginx=${NGINX_VERSION} && \