FIX: move the BatchNormalization before the activation with no bias

[glemaitre]

close #521

[pep8speaks]

Hello @glemaitre! Thanks for submitting the PR.

• In the file examples/applications/porto_seguro_keras_under_sampling.py, following are the PEP8 issues :

Line 27:1: E402 module level import not at top of file
Line 28:1: E402 module level import not at top of file
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Line 86:1: E402 module level import not at top of file
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Line 128:1: E402 module level import not at top of file
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Line 185:1: E402 module level import not at top of file
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Line 221:1: E402 module level import not at top of file