doc: Move Modula 2 PM4 link to https

gcc:
	* doc/gm2.texi (Dialect): Move PM4 link to https.

Author: GeraldPfeifer

gcc/doc/gm2.texi

@@ -1382,7 +1382,7 @@ The language as defined in 'Programming in Modula-2' 2nd Edition,
 Springer Verlag, 1982, 1983 by Niklaus Wirth (PIM2), 'Programming in
 Modula-2', 3rd Corrected Edition, Springer Verlag, 1985 (PIM3) and
 'Programming in Modula-2', 4th Edition, Springer Verlag, 1988 (PIM4)
-@uref{http://freepages.modula2.org/report4/modula-2.html} and the ISO
+@uref{https://freepages.modula2.org/report4/modula-2.html} and the ISO
 Modula-2 language as defined in ISO/IEC Information technology -
 programming languages - part 1: Modula-2 Language, ISO/IEC 10514-1
 (1996) (ISO).