cmd/go: fix two formatting issues in documentation of testing flags

Remove unneeded second colon.

Remove unneeded space at the beginning of a line (before a tab).

Regenerate alldocs.go with mkalldocs.sh.

Updates https://golang.org/cl/28783.
Updates https://golang.org/cl/29650.
Fixes #18448.

Change-Id: I1830136a2b760827d4cec565744807a0fd147584
Reviewed-on: https://go-review.googlesource.com/34718Reviewed-by: Rob Pike <r@golang.org>

src/cmd/go/alldocs.go

@@ -1474,7 +1474,7 @@
 // 	    text from Log and Logf calls even if the test succeeds.
 //
 // The following flags are also recognized by 'go test' and can be used to
-// profile the tests during execution::
+// profile the tests during execution:
 //
 // 	-benchmem
 // 	    Print memory allocation statistics for benchmarks.

src/cmd/go/test.go

@@ -200,7 +200,7 @@ const testFlag2 = `
 	    text from Log and Logf calls even if the test succeeds.
 
 The following flags are also recognized by 'go test' and can be used to
-profile the tests during execution::
+profile the tests during execution:
 
 	-benchmem
 	    Print memory allocation statistics for benchmarks.