Sanitize inputs

[adborden]

librato.timing(123.456)

Uncaught TypeError: Object 824888000 has no method 'replace'
at sanitize_name (/Users/adborden/goodeggs/egglightenment/node_modules/librato-node/lib/librato.js:75:17)
at EventEmitter.librato.timing (/Users/adborden/goodeggs/egglightenment/node_modules/librato-node/lib/librato.js:36:12)
at Stats.timing (/Users/adborden/goodeggs/egglightenment/lib/index.js:72:43)
at Object. (/Users/adborden/goodeggs/egglightenment/lib/response_time.js:16:20)
at Object.immediate._onImmediate (timers.js:348:16)
at processImmediate as _immediateCallback

Could throw an error that it expects a string, followed by number.