remove unnecessary array/each

tasks/toolchains/visualcpp.rake

@@ -1,5 +1,5 @@
 MRuby::Toolchain.new(:visualcpp) do |conf, _params|
-  [conf.cc].each do |cc|
+  conf.cc do |cc|
     cc.command = ENV['CC'] || 'cl.exe'
     # C4013: implicit function declaration
     cc.flags = [ENV['CFLAGS'] || %w(/c /nologo /W3 /we4013 /Zi /MD /O2 /D_CRT_SECURE_NO_WARNINGS)]
@@ -9,7 +9,7 @@ MRuby::Toolchain.new(:visualcpp) do |conf, _params|
     cc.compile_options = "%{flags} /Fo%{outfile} %{infile}"
   end
 
-  [conf.cxx].each do |cxx|
+  conf.cxx do |cxx|
     cxx.command = ENV['CXX'] || 'cl.exe'
     cxx.flags = [ENV['CXXFLAGS'] || ENV['CFLAGS'] || %w(/c /nologo /W3 /Zi /MD /O2 /EHs /D_CRT_SECURE_NO_WARNINGS)]
     cxx.defines = %w(DISABLE_GEMS MRB_STACK_EXTEND_DOUBLING)