Move text make valid to setConfig method

[johnfercher]

Description

• Move text make valid to setConfig method

Related Issue

378

Checklist

check with "x", if applied to your change

• [x] All methods associated with structs has func (<first letter of struct> *struct) method() {} name style.
• [x] Wrote unit tests for new/changed features.
• [x] Followed the unit test when,should naming pattern.
• [ ] Updated docs/doc.go and docs/*
• [ ] Updated pkg/pdf/example_test.go
• [ ] Updated README.md
• [x] Executed make examples to update all examples inside docs/examples.
• [ ] New public methods/structs/interfaces has comments upside them explaining they responsibilities
• [ ] Executed make dod with none issues pointed out by golangci-lint

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b3fc26e) 79.80% compared to head (0a2823e) 79.80%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #379 +/- ## ======================================= Coverage 79.80% 79.80% ======================================= Files 61 61 Lines 2009 2009 ======================================= Hits 1603 1603 Misses 378 378 Partials 28 28 ``` | [Flag](https://app.codecov.io/gh/johnfercher/maroto/pull/379/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=John+Fercher) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/johnfercher/maroto/pull/379/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=John+Fercher) | `79.80% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=John+Fercher#carryforward-flags-in-the-pull-request-comment) to find out more.

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