Resolve some instances of cppcoreguidelines-pro-type-member-init

https://github.com/dtolnay/cxx/issues/500
diff --git a/src/cxx.cc b/src/cxx.cc
index 122f6a5..c954513 100644
--- a/src/cxx.cc
+++ b/src/cxx.cc
@@ -67,8 +67,7 @@
   cxxbridge1$string$clone(this, other);
 }
 
-String::String(String &&other) noexcept {
-  this->repr = other.repr;
+String::String(String &&other) noexcept : repr(other.repr) {
   cxxbridge1$string$new(&other);
 }