Set clause coverage to true by default

Summary:
As title, update docs accordingly.

Leaving the `--clause-coverage` option in for now (it doesn't do anything) as it will be useful for coverage of non-top-level clauses.

Can be overridden by `EQWALIZER_CLAUSE_COVERAGE=false`.

Reviewed By: michalmuskala

Differential Revision: D59574467

fbshipit-source-id: 0ba77be16b81b29d1b7edc331a4da9e2e2fe4696

Author: VLanvin

docs/reference/advanced.md

@@ -175,6 +175,6 @@ attempt to detect and report redundant type assertions. See [redundant_guard err
 
 ### Spec coverage of function clauses
 
-Enable checks of proper coverage of function clauses by specs using `EQWALIZER_CLAUSE_COVERAGE=true`.
-By default, eqWAlizer will not check coverage of function clauses by the corresponding spec,
-hence a clause may be implicitly left unchecked.
+Disable checks of proper coverage of function clauses by specs using `EQWALIZER_CLAUSE_COVERAGE=false`.
+By default, eqWAlizer will check coverage of function clauses by the corresponding spec,
+ensuring all clauses are properly checked.

eqwalizer/src/main/resources/application.conf

@@ -17,6 +17,6 @@ eqwalizer {
     mode = ${?EQWALIZER_MODE}
     error_depth = 4
     error_depth = ${?EQWALIZER_ERROR_DEPTH}
-    clause_coverage = false
+    clause_coverage = true
     clause_coverage = ${?EQWALIZER_CLAUSE_COVERAGE}
 }