fix strip trailing whitespace for make_docs script (#4597)

docs/commands/each.md

@@ -8,11 +8,12 @@ Run a block on each element of input
 
 ## Signature
 
-```> each (block) --numbered```
+```> each (block) --keep-empty --numbered```
 
 ## Parameters
 
  -  `block`: the block to run
+ -  `--keep-empty`: keep empty result cells
  -  `--numbered`: iterate with an index
 
 ## Examples
@@ -21,3 +22,13 @@ Multiplies elements in list
 ```shell
 > [1 2 3] | each { |it| 2 * $it }
 ```
+
+Iterate over each element, keeping only values that succeed
+```shell
+> [1 2 3] | each { |it| if $it == 2 { echo "found 2!"} }
+```
+
+Iterate over each element, keeping all results
+```shell
+> [1 2 3] | each --keep-empty { |it| if $it == 2 { echo "found 2!"} }
+```