tools: depend on split in hledger.cabal just to make dev builds easier

hledger.cabal

@@ -87,6 +87,7 @@ executable hledger
                  ,process
                  ,regexpr >= 0.5.1
                  ,safe >= 0.2
+                 ,split == 0.1.*
                  ,time
                  ,utf8-string >= 0.3.5 && < 0.4
 
@@ -150,6 +151,7 @@ library
                  ,process
                  ,regexpr >= 0.5.1
                  ,safe >= 0.2
+                 ,split == 0.1.*
                  ,time
                  ,utf8-string >= 0.3.5 && < 0.4