Update CMakeLists.txt

[LocutusOfBorg]

Require at least cmake 3.11 to run examples, as its required in main CMakeLists.txt file. Newer cmake issue errors with version less then 3.5 See e.g. https://bugs.debian.org/1040723

[coveralls]

Pull Request Test Coverage Report for Build 5609465115

• 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 86.251%

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Totals
Change from base Build 5321226093:	0.0%
Covered Lines:	803
Relevant Lines:	931

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💛 - Coveralls

[gummif]

Thanks