fix: update Micro Focus Object COBOL broken url (#6604)

Resolves EbookFoundation/free-programming-books#6528

books/free-programming-books-langs.md

@@ -563,7 +563,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [COBOL Programming Fundamental](http://yusman.staff.gunadarma.ac.id/Downloads/files/33460/COBOL_Programming_Fundamental.pdf) (PDF)
 * [Enterprise COBOL for z/OS documentation library](http://www-01.ibm.com/support/docview.wss?uid=swg27036733)
 * [ILE COBOL Programmer's Guide](https://www.ibm.com/docs/de/ssw_ibm_i_74/pdf/sc092539.pdf) (PDF)
-* [Introduction to the COBOL Language](https://supportline.microfocus.com/documentation/books/oc41books/lrintr.htm)
+* [Micro Focus: OO Programming with Object COBOL for UNIX (1999)](https://www.microfocus.com/documentation/object-cobol/oc41books/oppubb.htm) - MERANT International Ltd. (HTML)
 * [OpenCOBOL 1.1 - Programmer's Guide](http://open-cobol.sourceforge.net/guides/OpenCOBOL%20Programmers%20Guide.pdf) (PDF)