Update PfxBuilder.cs

[zhaixiaowai]

The default Cert Algorithm of Org.BouncyCastle.Pkcs.Pkcs12StoreBuilder is PkcsObjectIdentifiers.PbewithShaAnd40BitRC2Cbc

Android devices do not support RC2's pfx certificate by default, so the modified method here passes the Cert Algorithm into the custom Cert Algorithm of the exported PFX file.

For example: pfxBuilder.Build(friendlyName, pfxPassword, PkcsObjectIdentifiers.PbeWithShaAnd3KeyTripleDesCbc)

Description

Please describe the purpose of the pull request.

Checklist

• [ ] All tests are passing
• [ ] New tests were created to address changes in pr (and tests are passing)
• [ ] Updated README and/or documentation, if necessary

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