Can't set the y-axis label in hydrograph_plot

Session Info

```r Session info -------------------------------------------------------------------------------------------------------------------------- setting value version R version 3.4.4 (2018-03-15) system x86_64, linux-gnu ui RStudio (1.1.423) language (EN) collate en_CA.UTF-8 tz America/Regina date 2018-05-23 Packages ------------------------------------------------------------------------------------------------------------------------------ package * version date source backports 1.1.2 2017-12-13 cran (@1.1.2) base * 3.4.4 2018-03-16 local compiler 3.4.4 2018-03-16 local CSHShydRology * 0.0.1 2018-05-23 local datasets * 3.4.4 2018-03-16 local devtools 1.13.5 2018-02-18 CRAN (R 3.4.3) digest 0.6.15 2018-01-28 CRAN (R 3.4.3) evaluate 0.10.1 2017-06-24 CRAN (R 3.4.1) graphics * 3.4.4 2018-03-16 local grDevices * 3.4.4 2018-03-16 local htmltools 0.3.6 2017-04-28 CRAN (R 3.4.1) knitr 1.20 2018-02-20 CRAN (R 3.4.3) lubridate 1.7.3 2018-02-27 CRAN (R 3.4.3) magrittr 1.5 2014-11-22 CRAN (R 3.4.1) memoise 1.1.0 2017-04-21 CRAN (R 3.4.1) methods * 3.4.4 2018-03-16 local Rcpp 0.12.16 2018-03-13 CRAN (R 3.4.4) rmarkdown 1.9 2018-03-01 CRAN (R 3.4.3) rprojroot 1.3-2 2018-01-03 cran (@1.3-2) rsconnect 0.8.8 2018-03-09 CRAN (R 3.4.3) stats * 3.4.4 2018-03-16 local stringi 1.1.7 2018-03-12 CRAN (R 3.4.4) stringr 1.3.0 2018-02-19 CRAN (R 3.4.3) tools 3.4.4 2018-03-16 local utils * 3.4.4 2018-03-16 local withr 2.1.2 2018-03-15 CRAN (R 3.4.4) yaml 2.1.18 2018-03-08 CRAN (R 3.4.3) ```

When I try to change the y-axis title, it fails. The last chunk in the attached pdf shows the issue

hydrograph_plot.pdf

CSHS-CWRA / CSHShydRology

Can't set the y-axis label in hydrograph_plot #3