fix: (isMobilePhone) add El Salvador validation

* Solve issue with wrong validation on El Salvador mobile phones
* update tests accordingly

in order to define the right regEx, the following site was
consulted.

https://www.siget.gob.sv/guia-de-servicios/consulta-el-plan-de-numeracion/numeros-moviles/

Author: hereje

src/lib/isMobilePhone.js

@@ -67,7 +67,7 @@ const phones = {
   'es-MX': /^(\+?52)?(1|01)?\d{10,11}$/,
   'es-PA': /^(\+?507)\d{7,8}$/,
   'es-PY': /^(\+?595|0)9[9876]\d{7}$/,
-  'es-SV': /^(\+?503)?\d{7,8}$/,
+  'es-SV': /^(\+?503)?[67]\d{7}$/,
   'es-UY': /^(\+598|0)9[1-9][\d]{6}$/,
   'es-VE': /^(\+?58)?(2|4)\d{9}$/,
   'et-EE': /^(\+?372)?\s?(5|8[1-4])\s?([0-9]\s?){6,7}$/,

test/validators.js

@@ -7164,15 +7164,19 @@ describe('Validators', () => {
       {
         locale: 'es-SV',
         valid: [
-          '+5032136663',
-          '+50321366634',
-          '+50321367217',
-          '+50321367460',
-          '+50321367632',
-          '+50321367767',
-          '+50321368314',
+          '62136634',
+          '50361366631',
+          '+50361366634',
+          '+50361367217',
+          '+50361367460',
+          '+50371367632',
+          '+50371367767',
+          '+50371368314',
         ],
         invalid: [
+          '+5032136663',
+          '21346663',
+          '+50321366663',
           '12345',
           'El salvador',
           'this should fail',