Add er.hideDef: for hiding relation definition

[k1LoW]

Fix #359

[github-actions]

Code Metrics Report

	main (e2de542)	#417 (db03ab4)	+/-
Coverage	67.1%	64.9%	-2.2%
Code to Test Ratio	1:0.4	1:0.4	+0.0
Test Execution Time	3m56s	3m5s	-51s

Details

  |                     | main (e2de542) | #417 (db03ab4) |  +/-  |
  |---------------------|----------------|----------------|-------|
- | Coverage            |          67.1% |          64.9% | -2.2% |
  |   Files             |             35 |             35 |     0 |
  |   Lines             |           3397 |           3397 |     0 |
- |   Covered           |           2280 |           2205 |   -75 |
+ | Code to Test Ratio  |          1:0.4 |          1:0.4 |  +0.0 |
  |   Code              |           8854 |           8863 |    +9 |
+ |   Test              |           3741 |           3765 |   +24 |
+ | Test Execution Time |          3m56s |           3m5s |  -51s |

Code coverage of files in pull request scope (72.9% → 72.9%)

Files	Coverage	+/-
config/config.go	71.5%	0.0%
output/dot/dot.go	76.3%	0.0%
output/mermaid/mermaid.go	76.3%	0.0%
output/plantuml/plantuml.go	77.2%	0.0%

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Reported by octocov