Fix the example 'default_provides'

The example should be declaring that the whole result is 'a'
and not just the first element of the returned result (which
in this case is the string index[0] which is also 'a') to
avoid propagating bad/broken patterns in the examples.

Fixes bug 1383422

Change-Id: I3a39bb25291276d29ee260e84aab9ec182499fd9
Merge "Fix the example 'default_provides'"