fix(isSlug): restrict allowed characters to valid slug charset

src/lib/isSlug.js

@@ -1,6 +1,6 @@
 import assertString from './util/assertString';
 
-let charsetRegex = /^[^\s-_](?!.*?[-_]{2,})[a-z0-9-\\][^\s]*[^-_\s]$/;
+let charsetRegex = /^[a-z0-9](?!.*[-_]{2,})(?:[a-z0-9_-]*[a-z0-9])?$/;
 
 export default function isSlug(str) {
   assertString(str);

test/validators.test.js

@@ -14187,13 +14187,15 @@ describe('Validators', () => {
     test({
       validator: 'isSlug',
       valid: [
+        'f',
+        'fo',
         'foo',
         'foo-bar',
         'foo_bar',
         'foo-bar-foo',
         'foo-bar_foo',
-        'foo-bar_foo*75-b4r-**_foo',
-        'foo-bar_foo*75-b4r-**_foo-&&',
+        'foo-75-b4r-foo',
+        'a1-b2_c3',
       ],
       invalid: [
         'not-----------slug',
@@ -14203,6 +14205,12 @@ describe('Validators', () => {
         '_not-slug',
         'not-slug_',
         'not slug',
+        'i.am.not.a.slug',
+        'slug.is.cool',
+        'foo-bar_foo*75-b4r-**_foo',
+        'foo-bar_foo*75-b4r-**_foo-&&',
+        'Foo-Bar',
+        'a:b',
       ],
     });
   });