Split after "=>" if the parameters split.

CHANGELOG.md

 # 0.2.0
 
 * **BREAKING:** The `indent` argument to `new DartFormatter()` is now a number
   of *spaces*, not *indentation levels*.
 
 * This version introduces a new n-way constraint system replacing the previous
   binary constraints. It's mostly an internal change, but allows us to fix a
   number of bugs that the old solver couldn't express solutions to.
 
   In particular, it forces argument and parameter lists to go one-per-line if
@@ skipping 11 matching lines @@
 * More precisely control newlines between declarations (#173).
 * Nest cascades like expressions (#200, #203, #205, #221, #236).
 * Do not nest blocks inside single-argument function and method calls.
 * Do nest blocks inside `=>` functions.
 * Set failure exit code for malformed input when reading from stdin (#359).
 * Indent cascades more deeply when the receiver is a method call (#137).
 * Prefer splitting at "." on non-identifier method targets (#161).
 * Nest blocks deeper inside a wrapped conditional operator (#186).
 * Split named arguments if the positional arguments split (#189).
 * Prefer splitting after `=>` over other options (#217).
+* If a `=>` function's parameters split, split after the `=>` too (#250).
 
 # 0.1.8
 
 * Update to latest `analyzer` and `args` packages.
 * Allow cascades with repeated method names to be one line.
 
 # 0.1.7
 
 * Update to latest analyzer (#177).
 * Don't discard annotations on initializing formals (#197).
@@ skipping 43 matching lines @@
 
 # 0.1.2
 
 * Move split conditional operators to the beginning of the next line.
 
 # 0.1.1
 
 * Support formatting enums (#120).
 * Handle Windows line endings in multiline strings (#126).
 * Increase nesting for conditional operators (#122).