Add update.sh script to easily update all the versions we support

[tianon]

Output looks like:

$ ./update.sh
+ sed -ri 's/^(ENV NODE_VERSION ).*/\10.10.30/' 0.10/Dockerfile
+ sed -ri 's/^(ENV NODE_VERSION ).*/\10.11.13/' 0.11/Dockerfile
+ sed -ri 's/^(ENV NODE_VERSION ).*/\10.8.28/' 0.8/Dockerfile

[tianon]

One sec, gonna shift the whitespace so the output doesn't have so many confusing 10s in it. :)

[tianon]

Updated output:

$ ./update.sh 
+ sed -ri 's/^(ENV NODE_VERSION) .*/\1 0.10.30/' 0.10/Dockerfile
+ sed -ri 's/^(ENV NODE_VERSION) .*/\1 0.11.13/' 0.11/Dockerfile
+ sed -ri 's/^(ENV NODE_VERSION) .*/\1 0.8.28/' 0.8/Dockerfile

[yosifkit]

LGTM