Need to include transpiled js artifacts in final build (#618)

v0.2.5 was bad (I deprecated it) because it was missing the transpiled orderbook.js file. I'm not sure why it was working when using yalc locally. I assume it is some kind of caching issue.

### Test Plan

yalc publish and verify that `typescript/common/{orderbook|fraction}.js` are present

package.json

@@ -1,6 +1,6 @@
 {
  "name": "@gnosis.pm/dex-contracts",
- "version": "0.2.5",
+ "version": "0.2.6",
  "description": "Contracts for dFusion multi-token batch auction exchange",
  "main": "src/index.js",
  "module": "typescript/esm/index.js",
@@ -50,6 +50,7 @@
  "build/contracts/SnappBaseCore.json",
  "build/contracts/TokenConservation.json",
  "build/types",
+ "typescript/common",
  "networks.json",
  "src"
  ],