Add missing \since to QSslCipher QString overload.

This was added in 5.3 in 30d199a76c.

Change-Id: I35a209fcfe417cb14605c4db19a3d2e85b67ee49
Reviewed-by: Michał Dutkiewicz
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/network/ssl/qsslcipher.cpp

@@ -71,6 +71,8 @@ QSslCipher::QSslCipher()
 }
 
 /*!
+    \since 5.3
+
     Constructs a QSslCipher object for the cipher determined by \a
     name. The constructor accepts only supported ciphers (i.e., the
     \a name must identify a cipher in the list of ciphers returned by