Update metric-types.md: typo (prometheus#900)

Signed-off-by: Sean Roberts <[email protected]>

Author: seanorama

docs/content/getting-started/metric-types.md

@@ -54,7 +54,7 @@ Histogram
 Histograms are for observing distributions, like latency distributions for HTTP services or the distribution of request sizes.
 Unlike with counters and gauges, each histogram data point has a complex data structure representing different aspects of the distribution:
 
-* Count: The toal number of observations.
+* Count: The total number of observations.
 * Sum: The sum of all observed values, e.g. the total time spent serving requests.
 * Buckets: The histogram buckets representing the distribution.