Add skip_serializing_if support for attributes

[olvyko]

Before that change skip_serializing_if won't work for struct fields that marked as attribute.
I changed ser_wrap_default_attribute func and added test for that change.

[coveralls]

Pull Request Test Coverage Report for Build 273

• 17 of 24 (70.83%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 59.895%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
yaserde_derive/src/lib.rs	0	2	0.0%
yaserde_derive/src/common/field.rs	0	5	0.0%

Files with Coverage Reduction	New Missed Lines	%
yaserde_derive/src/common/field.rs	1	0%

Totals
Change from base Build 272:	0.3%
Covered Lines:	1141
Relevant Lines:	1905

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💛 - Coveralls

[enfipy]

Any news on this?

[enfipy]

@MarcAntoine-Arnaud Thanks! Can you also publish a new version? It will help us publish android-manifest to crates.

[MarcAntoine-Arnaud]

Done with the 0.7.0, sorry for the delay.