expand_dims() signature change (and slight doc fix) (#331)

* Fix incorrect output shape behaviour in `expand_dims()`

* Keep `expand_dims()` signature in-line with `squeeze()`

Author: honno

spec/API_specification/manipulation_functions.md

@@ -39,7 +39,7 @@ Joins a sequence of arrays along an existing axis.
         ```
 
 (function-expand_dims)=
-### expand_dims(x, /, *, axis)
+### expand_dims(x, /, axis)
 
 Expands the shape of an array by inserting a new axis (dimension) of size one at the position specified by `axis`.
 
@@ -57,7 +57,7 @@ Expands the shape of an array by inserting a new axis (dimension) of size one at
 
 -   **out**: _<array>_
 
-    -   an expanded output array having the same data type and shape as `x`.
+    -   an expanded output array having the same data type as `x`.
 
 (function-flip)=
 ### flip(x, /, *, axis=None)