Year format of denominator pops not checked in developer annual updates doc 

Line 54 in 'vignettes/developer_annual_data_updates.Rmd'

```
janitor::compare_df_cols(population_counts, fpemlocal::population_counts, return = "mismatch")
```

does not catch a different format for the years column. Years should be in format "1970", "1971", etc., but passing in a data frame with years coded as "1970.5", "1971.5", etc., does not cause an exception. 