Include the unrecognized string in the error message

Author: alcuadrado

src/bytes.ts

@@ -76,7 +76,7 @@ export const toBuffer = function(v: any): Buffer {
         v = Buffer.from(ethjsUtil.padToEven(ethjsUtil.stripHexPrefix(v)), 'hex')
       } else {
         throw new Error(
-          'Cannot convert string to buffer. toBuffer only supports 0x-prefixed hex strings.',
+          `Cannot convert string to buffer. toBuffer only supports 0x-prefixed hex strings and this string was given: ${v}`,
         )
       }
     } else if (typeof v === 'number') {

test/index.js

@@ -507,9 +507,9 @@ describe('toBuffer', function () {
   })
 
   it('should fail with non 0x-prefixed hex strings', function() {
-    assert.throws(() => ethUtils.toBuffer('11'))
+    assert.throws(() => ethUtils.toBuffer('11'), '11')
     assert.throws(() => ethUtils.toBuffer(''))
-    assert.throws(() => ethUtils.toBuffer('0xR'))
+    assert.throws(() => ethUtils.toBuffer('0xR'), '0xR')
   })
 })