Fix typo

Co-authored-by: Antoine Lamirault <lantoine37@hotmail.fr>

Author: tcoch

string.rst

@@ -234,7 +234,7 @@ Methods to Change Case
     u('Foo: Bar-baz.')->snake(); // 'foo_bar_baz'
     // changes all graphemes/code points to kebab-case
     u('Foo: Bar-baz.')->kebab(); // 'foo-bar-baz'
-    // changes all graphemes/code points to pascal-case
+    // changes all graphemes/code points to PascalCase
     u('Foo: Bar-baz.')->pascal(); // 'FooBarBaz'
     // other cases can be achieved by chaining methods, e.g. :
     u('Foo: Bar-baz.')->camel()->upper(); // 'FOOBARBAZ'