[librsvg] tests/README.md: Rename rust/ to rsvg_internals/

[Federico Mena Quintero <federico src gnome org>]

commit e2263b643200f548b597e8049f97d143c6d4ac49
Author: Federico Mena Quintero <federico gnome org>
Date:   Fri Feb 23 15:57:07 2018 -0600

    tests/README.md: Rename rust/ to rsvg_internals/

 tests/README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/tests/README.md b/tests/README.md
index 533048bc..b703b75c 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -66,7 +66,7 @@ tests and the black box tests in this `librsvg/tests` directory.
 
 If you want to run just the black box tests, go into this
 `librsvg/tests` directory and run `make check`.  If you want to run
-the unit tests, go to `librsvg/rust` and run `cargo test`.
+the unit tests, go to `librsvg/rsvg_internals` and run `cargo test`.
 
 Those commands will yield exit code 0 if all the tests pass, or
 nonzero if some tests fail.