Switch to explicit find in modernize script

scripts/modernize.sh

@@ -3,4 +3,17 @@
 # Runs the Clang Modernizer in parallel on the code base.
 # Requires a compilation database in the build directory.
 
-git ls-files '*.cpp' | xargs -I{} -P $(nproc) clang-modernize -p build -final-syntax-check -format -style=file -summary -for-compilers=clang-3.4,gcc-4.8 -include . -exclude third_party {}
+find src include unit_tests -type f -name '*.hpp' -o -name '*.cpp' \
+  | xargs \
+      -I{} \
+      -P $(nproc) \
+      clang-modernize \
+        -p build \
+        -final-syntax-check \
+        -format \
+        -style=file \
+        -summary \
+        -for-compilers=clang-3.4,gcc-4.8 \
+        -include . \
+        -exclude third_party \
+      {}