installation: 2014_08_12_format upgrade recipe fix

• Fixes upgrade recipe invenio_2014_08_12_format_code_varchar20 that was not setting NOT NULL property on modified format.code column. (Not fully necessary, since the type is not relied upon in the application logic, but good for literal comparisons.)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>