use diff -u in driver.sh test

this changs the add/delete indication from
>
>
<
to
+
+
-
(same as git diff)

Author: matthiaskrgr

.github/driver.sh

@@ -24,18 +24,18 @@ unset CARGO_MANIFEST_DIR
 # FIXME: How to match the clippy invocation in compile-test.rs?
 ./target/debug/clippy-driver -Dwarnings -Aunused -Zui-testing --emit metadata --crate-type bin tests/ui/double_neg.rs 2> double_neg.stderr && exit 1
 sed -e "s,tests/ui,\$DIR," -e "/= help/d" double_neg.stderr > normalized.stderr
-diff normalized.stderr tests/ui/double_neg.stderr
+diff -u normalized.stderr tests/ui/double_neg.stderr
 
 
 # make sure "clippy-driver --rustc --arg" and "rustc --arg" behave the same
 SYSROOT=`rustc --print sysroot`
-diff <(LD_LIBRARY_PATH=${SYSROOT}/lib ./target/debug/clippy-driver --rustc --version --verbose) <(rustc --version --verbose)
+diff -u <(LD_LIBRARY_PATH=${SYSROOT}/lib ./target/debug/clippy-driver --rustc --version --verbose) <(rustc --version --verbose)
 
 
 echo "fn main() {}" > target/driver_test.rs
 # we can't run 2 rustcs on the same file at the same time
 CLIPPY=`LD_LIBRARY_PATH=${SYSROOT}/lib ./target/debug/clippy-driver ./target/driver_test.rs --rustc`
 RUSTC=`rustc ./target/driver_test.rs`
-diff <($CLIPPY) <($RUSTC)
+diff -u <($CLIPPY) <($RUSTC)
 
 # TODO: CLIPPY_CONF_DIR / CARGO_MANIFEST_DIR