Breaking: deprecate safe-buffer.Buffer calls (#110)

safe-buffer.Buffer function/constructror is just a re-export of
buffer.Buffer and should be deprecated likewise.

Otherwise, using Buffer = require('safe-buffer').Buffer magically hides
the deprecation message, which it shouldn't, as that code will
actually cause runtime deprecation errors on Node.js >= 10.

lib/util/deprecated-apis.js

@@ -417,3 +417,7 @@ module.exports = {
         },
     },
 }
+
+// safe-buffer.Buffer function/constructror is just a re-export of buffer.Buffer
+// and should be deprecated likewise.
+module.exports.modules["safe-buffer"] = module.exports.modules.buffer