refactor(signer): remove unused catch binding (#315)

signer.js

@@ -36,7 +36,7 @@ function validateAlgorithm (algorithm) {
   // validate that the algorithm is supported by the node runtime
   try {
     crypto.createHmac(algorithm, crypto.randomBytes(16))
-  } catch (e) {
+  } catch {
     throw new TypeError(`Algorithm ${algorithm} not supported.`)
   }
 }