Upgrade etcher-image-write to v5.0.1 (#469)

* Upgrade etcher-image-write to v5.0.1

The new version contains an important fix to prevent `EPERM` errors on
Windows with certain drives.

Fixes: #334
Signed-off-by: Juan Cruz Viotti <jviottidc@gmail.com>

* Upgrade NPM to fix newer package versions not available in Appveyor

See: npm/npm#4984
Signed-off-by: Juan Cruz Viotti <jviottidc@gmail.com>

appveyor.yml

@@ -21,6 +21,7 @@ environment:
 
 install:
   - ps: Install-Product node $env:nodejs_version x64
+  - npm install -g npm
   - npm install --build-from-source
   - npm install -g bower
   - bower install

package.json

@@ -60,7 +60,7 @@
     "drivelist": "^3.2.0",
     "electron-is-running-in-asar": "^1.0.0",
     "etcher-image-stream": "^2.0.0",
-    "etcher-image-write": "^5.0.0",
+    "etcher-image-write": "^5.0.1",
     "flexboxgrid": "^6.3.0",
     "is-elevated": "^1.0.0",
     "lodash": "^4.5.1",