Don't allow histogram bins contain dots

lib/process_metrics.js

@@ -122,7 +122,7 @@ var process_metrics = function (metrics, flushInterval, ts, flushCallback) {
           for (; i < count && (bins[bin_i] == 'inf' || values[i] < bins[bin_i]); i++) {
             freq += 1;
           }
-          bin_name = 'bin_' + bins[bin_i];
+          bin_name = 'bin_' + bins[bin_i].toString().replace('.', '_');
           current_timer_data['histogram'][bin_name] = freq;
         }
 

test/process_metrics_tests.js

@@ -192,7 +192,7 @@ module.exports = {
     // only 'abc' should have a bin_inf; also check all its counts,
     // and make sure it has no other bins
     test.equal(1, timer_data['abc']['histogram']['bin_1']);
-    test.equal(0, timer_data['abc']['histogram']['bin_2.21']);
+    test.equal(0, timer_data['abc']['histogram']['bin_2_21']);
     test.equal(4, timer_data['abc']['histogram']['bin_inf']);
     test.equal(3, _.size(timer_data['abc']['histogram']));