docs: improve signature malleability wording

Update comment to indicate these test vectors should only be used for
implementations that _do not_ allow signature malleability. If an
implementation tolerates or even requires malleability, it should be
tested with a different set of test vectors.

Author: josibake

testvectors_v1/ecdsa_secp256k1_sha256_bitcoin_test.json

@@ -95,7 +95,7 @@
     },
     "SignatureMalleabilityBitcoin" : {
       "bugType" : "SIGNATURE_MALLEABILITY",
-      "description" : "Signature malleability can be a serious issue in Bitcoin. An implementation should only accept a signature s where s < n/2. If an implementation is not meant for use cases that require signature malleability then this implementation should be tested with another set of test vectors.",
+      "description" : "Signature malleability can be a serious issue in Bitcoin. An implementation should only accept a signature s where s < n/2. If an implementation is meant for use cases that tolerate signature malleability then this implementation should not be tested with this set of test vectors.",
       "effect" : "In Bitcoin exchanges, it may be used to make a double deposits or double withdrawals",
       "links" : [
         "https://en.bitcoin.it/wiki/Transaction_malleability",