Webassets introduced the "auto_build" option in 0.7 and deprecated setting updater=never or updater=False . This patch adds the auto_build option as a boolean.
Adding an additional test assertion for "True" as the default value of auto_build, per webassets documentation.
Merge pull request #15 from zwant/master

Add support for the auto_build setting which was introduced in webassets 0.7