3.0 update timer bar creation

the `Cake\Utility\Number::precision()` doesn't return float anymore but string in 3.0
This causes that if a time value is over 1000ms, with the locale formating the conversion string to int in the `bar()` function will return 1 instead of 1000 (as the number is send to the function as a string like `1,834.24` in us or '1 834,24' in france).
Screenshot before the modification: 
![capture1](https://cloud.githubusercontent.com/assets/4977112/4131083/72f21d0a-3341-11e4-87b2-0fd18afc7d47.PNG)

after : 
![capture2](https://cloud.githubusercontent.com/assets/4977112/4131085/812a2106-3341-11e4-81c8-d3c12c4c474b.PNG)