Update to rscons-3.1.0

Rsconscript

@@ -7,17 +7,15 @@ configure do
   check_lib "freeimage"
 end
 
-build do
-  Environment.new do |env|
-    env["CCFLAGS"] += %w[-Wall -O2]
-    env["CPPPATH"] += glob("src/**")
+env do |env|
+  env["CCFLAGS"] += %w[-Wall -O2]
+  env["CPPPATH"] += glob("src/**")
 
-    env.CFile("^/parser/lexer.cc", "src/parser/parser.ll")
-    env.CFile("^/parser/parser.cc", "src/parser/parser.yy")
-    env["CPPPATH"] += ["#{env.build_root}/parser"]
+  env.CFile("^/parser/lexer.cc", "src/parser/parser.ll")
+  env.CFile("^/parser/parser.cc", "src/parser/parser.yy")
+  env["CPPPATH"] += ["#{env.build_root}/parser"]
 
-    sources = glob("src/**/*.cc")
-    sources += ["^/parser/lexer.cc", "^/parser/parser.cc"]
-    env.Program("fart", sources)
-  end
+  sources = glob("src/**/*.cc")
+  sources += ["^/parser/lexer.cc", "^/parser/parser.cc"]
+  env.Program("fart", sources)
 end