swapping base64 modes to match the rest (#446)

Author: barnjamin

pyteal/ir/ops.py

@@ -181,7 +181,7 @@ def min_version(self) -> int:
     acct_params_get     = OpType("acct_params_get",     Mode.Application,                  6)
     replace2            = OpType("replace2",            Mode.Signature | Mode.Application, 7)
     replace3            = OpType("replace3",            Mode.Signature | Mode.Application, 7)
-    base64_decode       = OpType("base64_decode",       Mode.Application | Mode.Signature, 7)
+    base64_decode       = OpType("base64_decode",       Mode.Signature | Mode.Application, 7)
     json_ref            = OpType("json_ref",            Mode.Signature | Mode.Application, 7)
     ed25519verify_bare  = OpType("ed25519verify_bare",  Mode.Signature | Mode.Application, 7)
     sha3_256            = OpType("sha3_256",            Mode.Signature | Mode.Application, 7)