fix(flow): Add ps-node as a dev dependency

It's used by flow:

Launching Flow server for /.../zap-desktop
Spawned flow server (pid=46193)
Logs will go to /private/tmp/flow/zSUserszSbenzSDevelopmentzSBitcoinzSzZap-desktop.log
app/main.dev.js:18
 18: import { lookup } from 'ps-node'
                            ^^^^^^^^^ ps-node. Required module not found

Found 1 error
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! zap-desktop@0.0.1 flow: `flow`
npm ERR! Exit status 2

package.json

@@ -171,6 +171,7 @@
     "jsdom": "^11.0.0",
     "minimist": "^1.2.0",
     "node-sass": "^4.5.3",
+    "ps-node": "^0.1.6",
     "react-addons-test-utils": "^15.6.0",
     "react-test-renderer": "^15.6.1",
     "redux-logger": "^3.0.6",

yarn.lock

@@ -2244,6 +2244,10 @@ connect-history-api-fallback@^1.3.0:
   version "1.3.0"
   resolved "https://registry.yarnpkg.com/connect-history-api-fallback/-/connect-history-api-fallback-1.3.0.tgz#e51d17f8f0ef0db90a64fdb47de3051556e9f169"
 
+connected-domain@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/connected-domain/-/connected-domain-1.0.0.tgz#bfe77238c74be453a79f0cb6058deeb4f2358e93"
+
 console-browserify@^1.1.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/console-browserify/-/console-browserify-1.1.0.tgz#f0241c45730a9fc6323b206dbf38edc741d0bb10"
@@ -7225,6 +7229,12 @@ prr@~0.0.0:
   version "0.0.0"
   resolved "https://registry.yarnpkg.com/prr/-/prr-0.0.0.tgz#1a84b85908325501411853d0081ee3fa86e2926a"
 
+ps-node@^0.1.6:
+  version "0.1.6"
+  resolved "https://registry.yarnpkg.com/ps-node/-/ps-node-0.1.6.tgz#9af67a99d7b1d0132e51a503099d38a8d2ace2c3"
+  dependencies:
+    table-parser "^0.1.3"
+
 pseudomap@^1.0.1, pseudomap@^1.0.2:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/pseudomap/-/pseudomap-1.0.2.tgz#f052a28da70e618917ef0a8ac34c1ae5a68286b3"
@@ -8657,6 +8667,12 @@ synesthesia@^1.0.1:
   dependencies:
     css-color-names "0.0.3"
 
+table-parser@^0.1.3:
+  version "0.1.3"
+  resolved "https://registry.yarnpkg.com/table-parser/-/table-parser-0.1.3.tgz#0441cfce16a59481684c27d1b5a67ff15a43c7b0"
+  dependencies:
+    connected-domain "^1.0.0"
+
 table@^3.7.8:
   version "3.8.3"
   resolved "https://registry.yarnpkg.com/table/-/table-3.8.3.tgz#2bbc542f0fda9861a755d3947fefd8b3f513855f"