Add IgnoreBaseInCopyConstructors to .clang-tidy

gcc issues warnings on copy constructors that do not explicitly
initialize the base class.
diff --git a/.clang-tidy b/.clang-tidy
index 3f2f2c0..1d4438d 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -16,4 +16,5 @@
     value:           CamelCase
   - key:             readability-identifier-naming.IgnoreMainLikeFunctions
     value:           1
-
+  - key:             readability-redundant-member-init.IgnoreBaseInCopyConstructors
+    value:           1