Widen signature on parse_platform (#194)

Author: vchuravy

src/Platforms.jl

@@ -41,7 +41,7 @@ platform_exeext(p::AbstractPlatform) = Sys.iswindows(p) ? ".exe" : ""
 
 # Helper parsing function: it extends `parse(Platform, p)` by supporting
 # `AnyPlatform` as well.
-parse_platform(p::String) = p == "any" ? AnyPlatform() : parse(Platform, p; validate_strict=true)
+parse_platform(p::AbstractString) = p == "any" ? AnyPlatform() : parse(Platform, p; validate_strict=true)
 
 
 # Recursively test for key presence in nested dicts