Fix benchmark generator (#107)

Author: mathiasbynens

benchmarks/add.mjs

@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import JSBI from '../jsbi';
+import JSBI from '../dist/jsbi.mjs';
 const JSBigInt = JSBI.BigInt;
 
 const kDataHex = [
@@ -1016,7 +1016,7 @@ const kDataHex = [
   '0xd9fdc391802e586780107c726b2497544645fceff4ffa5f70889582d50e4d857ffd2fe76',
   '0x8766de418627206fb60366530cafb0681e0b07e772018457b020f011dd1fef6663b0e1f8',
 ];
-var kDataDec = [
+const kDataDec = [
   '78268667896347885416699482883172282537169176645625607673273417204283519222',
   '27431633917963087836304206026541344025954548276389434071297449056207600387',
   '50147991596445303965480881232870021807123231994756807057128784840280369684',