patch 9.0.2056: no digraph for quadruple prime

Problem:  no digraph for quadruple prime
Solution: add quadruple prime digraph using 4'

closes: #13380

Signed-off-by: Jonathan Wright <quaggy@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Jonathan Wright <quaggy@gmail.com>
diff --git a/src/digraph.c b/src/digraph.c
index fb45c15..0a4a4a3 100644
--- a/src/digraph.c
+++ b/src/digraph.c
@@ -853,6 +853,7 @@
 	{'1', '\'', 0x2032},
 	{'2', '\'', 0x2033},
 	{'3', '\'', 0x2034},
+	{'4', '\'', 0x2057},
 	{'1', '"', 0x2035},
 	{'2', '"', 0x2036},
 	{'3', '"', 0x2037},