Add ERC20 decimal field support

src/abi/erc20.json

@@ -15,6 +15,14 @@
     "payable": false,
     "type": "function"
   },
+  {
+    "constant": true,
+    "inputs": [],
+    "name": "decimals",
+    "outputs": [{ "name": "", "type": "uint8" }],
+    "payable": false,
+    "type": "function"
+  },
   {
     "constant": true,
     "inputs": [],

src/erc20/model/index.ts

@@ -65,6 +65,13 @@ export class Erc20TokenContract {
       .call()
       .catch(() => undefined);
   }
+
+  public async decimals() {
+    return this._contract.methods
+      .decimals()
+      .call()
+      .catch(() => undefined);
+  }
 }
 
 export class Erc20TokenHolder {

src/erc20/schema/token.ts

@@ -8,5 +8,6 @@ type TokenContract {
   account: Account
   symbol: String
   totalSupply: Long
+  decimals: Int
 }
 `;