Give write permission to strings.json for all.

Appium fails due to insufficient write permissions for strings.json
on multi-user systems. 

I have a jenkins setup on my box (where Appium is run by the 'jenkins' user) and I get this error when I try to run Appium with my user:
```
debug: java -jar "/home/paymand/src/oppium/node_modules/appium/lib/devices/android/helpers/strings_from_apk.jar" "/home/paymand/Downloads/master-67315-release-final-armv7-androidmarket-lzma-14_inf.apk" "/tmp/com.opera.browser"
debug: Exception in thread "main" java.io.FileNotFoundException: /tmp/com.opera.browser/strings.json (Permission denied)
	at java.io.FileOutputStream.open(Native Method)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:212)
	at java.io.FileOutputStream.<init>(FileOutputStream.java:165)
	at strings.StringsXML.toJSON(StringsXML.java:44)
	at strings.StringsXML.run(StringsXML.java:100)
	at strings.StringsXML.main(StringsXML.java:151)
```

This fix makes sure everyone has write access to it.