Use "Environment" instead of "Rscons::Environment" in build tests

build_tests/custom_builder/Rsconscript

@@ -10,7 +10,7 @@ EOF
 end
 
 build do
-  Rscons::Environment.new do |env|
+  Environment.new do |env|
     env.add_builder(MySource.new)
     env.MySource('inc.h', [])
     env.Program('program.exe', Dir['*.c'])