fix short mention with single character followed by dot isn't recognized

Author: bernhardoj

__tests__/ExpensiMark-HTML-test.js

@@ -1530,6 +1530,12 @@ describe('Tests for short mentions', () => {
         const resultString = '<mention-short>@john.doe</mention-short><mention-here>@here</mention-here>';
         expect(parser.replace(testString)).toBe(resultString);
     });
+
+    test('short mentions should work for single character followed by dot', () => {
+        const testString = '@j.doe';
+        const resultString = '<mention-short>@j.doe</mention-short>';
+        expect(parser.replace(testString)).toBe(resultString);
+    });
 });
 
 // Examples that should match for here mentions:

lib/ExpensiMark.ts

@@ -503,7 +503,7 @@ export default class ExpensiMark {
                 name: 'shortMentions',
 
                 regex: new RegExp(
-                    `${Constants.CONST.REG_EXP.PRE_MENTION_TEXT_PART}(@(?=((?=[\\w]+[\\w'#%+-]+(?:\\.[\\w'#%+-]+)*)[\\w\\.'#%+-]{1,64}(?= |_|\\b))(?!([:\\/\\\\]))(?<end>.*))(?!here)\\S{3,254}(?=\\k<end>$))(?!((?:(?!<a).)+)?<\\/a>|[^<]*(<\\/pre>|<\\/code>|<\\/mention-user>|<\\/mention-here>))`,
+                    `${Constants.CONST.REG_EXP.PRE_MENTION_TEXT_PART}(@(?=((?=[\\w]+[\\w'#%+-]*(?:\\.[\\w'#%+-]+)*)[\\w\\.'#%+-]{1,64}(?= |_|\\b))(?!([:\\/\\\\]))(?<end>.*))(?!here)\\S{3,254}(?=\\k<end>$))(?!((?:(?!<a).)+)?<\\/a>|[^<]*(<\\/pre>|<\\/code>|<\\/mention-user>|<\\/mention-here>))`,
                     'gim',
                 ),
                 replacement: (_extras, match, g1, g2) => {