Update doc/specs/stdlib_math.md

Co-authored-by: Federico Perini <federico.perini@gmail.com>

Author: MilanSkocic

doc/specs/stdlib_math.md

@@ -392,7 +392,7 @@ Experimental
 
 Elemenal function.
 
-`deg2rad` converts the phase angle from degree to radian.
+`deg2rad` converts phase angles from degrees to radians.
 
 #### Syntax