Bump version also in source code

Change-Id: I3c60e888216bc8cb0264fe3c7c68a0cc670e43f1
diff --git a/src/dereko2vec.c b/src/dereko2vec.c
index 5b8ef43..9e9c02e 100644
--- a/src/dereko2vec.c
+++ b/src/dereko2vec.c
@@ -1924,7 +1924,7 @@
 }
 
 void print_help() {
-		printf("WORD VECTOR estimation toolkit v 0.9.0\n\n");
+		printf("WORD VECTOR estimation toolkit v 0.9.1\n\n");
 		printf("Options:\n");
 		printf("Parameters for training:\n");
 		printf("\t-train <file>\n");