Update examples for Rust master

ruby-to-rust/Makefile

@@ -4,12 +4,11 @@ else
     EXT := so
 endif
 
-all: target/libdouble_input.so
+all: target/debug/libdouble_input.$(EXT)
 	ruby src/main.rb
 
-target/libdouble_input.so: src/lib.rs Cargo.toml
+target/debug/libdouble_input.$(EXT): src/lib.rs Cargo.toml
 	cargo build
-	(cd target && ln -nsf debug/libdouble_input-*$(EXT) libdouble_input.so)
 
 clean:
 	rm -rf target