fix floats

just a minor typo (buffer.readFloadLE)

other than that im totaly sure why but the test still doesnt pass for me

```
# float encode + decode
not ok 7 should be equivalent
  ---
    operator: deepEqual
    expected: { float: 1.1 }
    actual:   { float: 1.100000023841858, float2: 0 }
    at: Test.Float.encode.float (/home/patrick/dev/lib/protocol-buffers/test/float.js:13:5)
  ...
# float encode + decode + negative
not ok 8 should be equivalent
  ---
    operator: deepEqual
    expected: { float: 0, float2: -1.1 }
    actual:   { float: 0, float2: -1.100000023841858 }
    at: Test.<anonymous> (/home/patrick/dev/lib/protocol-buffers/test/float.js:28:5)
  ...
```