sed.1: Correction for the case insensitive case.

Use the capital I instead of the lowercase.

Submitted by:	Mikhail T.
PR:		195929
MFC after:	2 weeks

usr.bin/sed/sed.1

@@ -31,7 +31,7 @@
 .\"	@(#)sed.1	8.2 (Berkeley) 12/30/93
 .\" $FreeBSD$
 .\"
-.Dd June 20, 2014
+.Dd May 10, 2016
 .Dt SED 1
 .Os
 .Sh NAME
@@ -198,7 +198,7 @@ option was specified);
 a context address
 that consists of a regular expression preceded and followed by a
 delimiter. The closing delimiter can also optionally be followed by the
-.Dq i
+.Dq I
 character, to indicate that the regular expression is to be matched
 in a case-insensitive way.
 .El