Fix NLPModels limit and update to version 0.6.2

[abelsiqueira]

Let's release 0.6.2 before merging #92 to limit NLPModels version on 0.6.x.

[coveralls]

Pull Request Test Coverage Report for Build 453

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.5%

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Totals
Change from base Build 451:	0.0%
Covered Lines:	398
Relevant Lines:	400

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💛 - Coveralls