[Style] Update timeseries to time series. (#11125)

**What this PR does / why we need it**:
Small update to conform to recent Style decision re: spelling of `time
series`.
https://grafana.com/docs/writers-toolkit/write/style-guide/word-list/#t

docs/sources/query/_index.md

@@ -290,7 +290,7 @@ Loki supports functions to operate on data.
 
 ### label_replace()
 
-For each timeseries in `v`,
+For each time series in `v`,
 
 ```
 label_replace(v instant-vector,
@@ -300,12 +300,12 @@ label_replace(v instant-vector,
     regex string)
 ```
 matches the regular expression `regex` against the label `src_label`.
-If it matches, then the timeseries is returned with the label `dst_label` replaced by the expansion of `replacement`.
+If it matches, then the time series is returned with the label `dst_label` replaced by the expansion of `replacement`.
 
 `$1` is replaced with the first matching subgroup,
 `$2` with the second etc.
 If the regular expression doesn't match,
-then the timeseries is returned unchanged.
+then the time series is returned unchanged.
 
 This example will return a vector with each time series having a `foo` label with the value `a` added to it: