The character in question  is the Unicode Character 'ZERO WIDTH NO-BREAK SPACE' (U+FEFF). It may be that you copied it into your code via a copy/paste without realizing it. The fact that it's not visible makes it hard to tell if you're using an editor that displays actual unicode characters.
One option is to open the file in a very basic text editor that doesn't understand unicode, or one that understands it but has the ability to display any non-ascii characters using their actual codes.
Once you locate it, you can delete the small block of text around it and retype that text manually.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
