docs(cite): fix doubled "is" in bibtex intro (#632)

Author: adv0r

en/cite/bibtex-and-biblatex.md

@@ -4,7 +4,7 @@ description: The data format of JabRef is BibTeX. In addtion JabRef also support
 
 # BibTeX and biblatex
 
-JabRef is is a program for working with BibTeX and biblatex libraries. JabRef program uses no separate internal file format but directly works with BibTeX and biblatex. That means, your BibTeX/biblatex file is kept as is when opening in JabRef and saving again: You normally load and save your libraries directly in the BibTeX/biblatex`.bib` format. In addition, you can also [import](../collect/) and export bibliography libraries in a number of other formats into JabRef.
+JabRef is a program for working with BibTeX and biblatex libraries. JabRef program uses no separate internal file format but directly works with BibTeX and biblatex. That means, your BibTeX/biblatex file is kept as is when opening in JabRef and saving again: You normally load and save your libraries directly in the BibTeX/biblatex`.bib` format. In addition, you can also [import](../collect/) and export bibliography libraries in a number of other formats into JabRef.
 
 The library mode can be changed in the [library properties](../setup/databaseproperties.md).