this code block is text not Rust code

Author: Jorge Aparicio

src/doc/unstable-book/src/linker-flavor.md

@@ -36,7 +36,7 @@ $ xargo rustc --target thumbv7m-none-eabi -- \
 
 Whereas the default is:
 
-```
+``` text
 $ xargo rustc --target thumbv7m-none-eabi -- \
     -C link-arg=-nostartfiles \
     -Z print-link-args | tr ' ' '\n'