refactor(Publications): fix 'PhD theses' section title

Refs #2

page_publications.Rmd

@@ -246,7 +246,7 @@ In: SGEM2018. 18th International Multidisciplinary Scientific GeoConference Surv
 - Astorayme Valenzuela M. & Felipe O. (2019). Hydrological Simulation Using Two High-Resolution Satellite Precipitation Products to Generate Hourly Discharge Rates in the Rimac Basin, Peru. In: World Environmental and Water Resources Congress 2019. Pittsburgh (United States of America). doi: [10.1061/9780784482339.029](https://doi.org/10.1061/9780784482339.029)
 
 
-## PhD thesis
+## PhD theses
 
 ### 2020