message: Fix docs proofreading
diff: @@ -179,7 +179,7 @@ series.applyOptions({
  #### Base line
  -The base line is a horizontal line drawn on the zero-level in percentage and indexedTo100 modes.
  +The base line is a horizontal line drawn at the zero-level in `percentage` and `indexedTo100` modes.
  You can set the width, style and color of this line or disable it using the following options:
  |Name|Type|Default|Description|
  