Update ExpressionEvaluator.cs

[LuanDevecchi]

Changing regex to accept "ç" and accentuation.

if we

vár = 123
or
varç = 123

and try to use it, a exception is thrown

CodingSeb.ExpressionEvaluator.ExpressionEvaluatorSyntaxErrorException: Variable [v] unknown in expression : [vár]

 CodingSeb.ExpressionEvaluator.ExpressionEvaluatorSyntaxErrorException: Variable [var] unknown in expression : [varç]

[codingseb]

Thanks for the suggestion. I will already merge it in the dev branch.
I will add some tests and it will be publish on master and as a nuget in the next version.