Fix Pro URL in contact-buttons-render-base

[szepeviktor]

PR Checklist

• [x] The commit message follows our guidelines: https://github.com/elementor/elementor/blob/master/.github/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation content changes
• [x] Other... Please describe: fix an URL

Summary

Without the trailing slash it produces a redirect.

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[szepeviktor]

@elementorbot stop

[toineenzo]

@elementorbot stop

Why are you arguing with a bot lol