fix: fix download failure for git repo with protocol 'git://'

[zong-zhe]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

fix #587

2. What is the scope of this PR (e.g. component or file name):

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

[coveralls]

Pull Request Test Coverage Report for Build 12805599629

Details

• 8 of 24 (33.33%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.001%) to 42.022%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/downloader/source.go	5	9	55.56%
pkg/downloader/downloader.go	3	15	20.0%

Totals
Change from base Build 12760666391:	-0.001%
Covered Lines:	4174
Relevant Lines:	9933

---

💛 - Coveralls

[He1pa]

lgtm