Diff is empty when lines are too long

On assert.Equal failures, if the diff has long lines (due to complicated structs), instead of showing something like

require.go:157:
                	Error Trace:	common_test.go:72
                	            				transactions_test.go:844
                	Error:      	Not equal:
					expected: ...
					actual: ...

					Diff:
					--- Expected
					+++ Actual
					<super long line...>
                	Test:       	TestTransactionsQueryFingerprint
                	Messages:   	Response does not match expected return

Currently the diff is completely cut off

require.go:157:
                	Error Trace:	common_test.go:72
                	            				transactions_test.go:844
                	Error:      	Not equal:
                	Test:       	TestTransactionsQueryFingerprint
                	Messages:   	Response does not match expected return

This makes testing hard to check which lines differed.

Upon inspecting, indentation formatting of diff lines is using bufio.Scanner which has a default MaxScanTokenSize (64K) and would not parse long lines: https://github.com/stretchr/testify/blob/master/assert/assertions.go#L201

Can be fixed by either changing from bufio.Scanner to bufio.Reader or truncating long lines up to the max token size (or even provide a config to change max). Thoughts?