fix positionMapping description

Author: soulomoon

ghcide/src/Development/IDE/Core/Shake.hs

@@ -266,7 +266,7 @@ data ShakeExtras = ShakeExtras
     -- ^ Map from a text document version to a PositionMapping that describes how to map
     -- positions in a version of that document to positions in the latest version
     -- First mapping is delta from previous version and second one is an
-    -- accumulation of all previous mappings.
+    -- accumulation to the current version.
     ,progress :: ProgressReporting
     ,ideTesting :: IdeTesting
     -- ^ Whether to enable additional lsp messages used by the test suite for checking invariants