Add modernize-use-default-member-init check.

.clang-tidy

@@ -1,7 +1,10 @@
 ---
-Checks:          '-*,readability-*,bugprone-*,misc-*,performance-*,modernize-redundant-void-arg,modernize-deprecated-headers,modernize-use-override,modernize-use-auto,modernize-use-nullptr,-readability-else-after-return,-readability-named-parameter,-readability-braces-around-statements,-readability-inconsistent-declaration-parameter-name,-readability-isolate-declaration,-readability-magic-numbers,-readability-convert-member-functions-to-static,-bugprone-macro-parentheses,-bugprone-narrowing-conversions,-bugprone-branch-clone,-misc-non-private-member-variables-in-classes,-misc-unused-parameters'
+Checks:          '-*,readability-*,bugprone-*,misc-*,performance-*,modernize-redundant-void-arg,modernize-deprecated-headers,modernize-use-override,modernize-use-auto,modernize-use-nullptr,modernize-use-default-member-init,-readability-else-after-return,-readability-named-parameter,-readability-braces-around-statements,-readability-inconsistent-declaration-parameter-name,-readability-isolate-declaration,-readability-magic-numbers,-readability-convert-member-functions-to-static,-bugprone-macro-parentheses,-bugprone-narrowing-conversions,-bugprone-branch-clone,-misc-non-private-member-variables-in-classes,-misc-unused-parameters'
 WarningsAsErrors: ''
 HeaderFilterRegex: '.*'
 AnalyzeTemporaryDtors: false
 FormatStyle:     file
+CheckOptions:
+  - key:   modernize-use-default-member-init.UseAssignment
+    value: 1
 ...