remove spaces from build string

[rminnich]

The embedded spaces in the build string make it very difficult to use u-root, as the shells tend to lose the quoting at some point. It's difficult to do triple-level quoting across every version of Make.

[abarisani]

Given that this is u-root specific, and that we are asking the u-root example to be on a separate repository than this one, we won't be applying this change as it can be overridden elsewhere.