Before this change, the `script` statement had inherited global defaults. After this change, it overrides them. The new behavior matches the behavior of makeotf v2.0.90. Resolves https://github.com/behdad/fonttools/issues/505. For the test case of https://github.com/behdad/fonttools/issues/501, which was about an unrelated problem, feaLib now produces the exact same output as makeotf v2.0.90.