codecov: fix error reporting printing

[vtjnash]

Previously, this would print an html page, now it will print the error message

Fixes #276

[codecov-io]

Codecov Report

Merging #293 (319daf5) into master (36fc28a) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #293   +/-   ##
=======================================
  Coverage   81.90%   81.90%           
=======================================
  Files           3        3           
  Lines         199      199           
=======================================
  Hits          163      163           
  Misses         36       36           

Impacted Files	Coverage Δ
src/codecovio.jl	76.08% <100.00%> (ø)

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[coveralls]

Pull Request Test Coverage Report for Build 934

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 82.803%

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Totals
Change from base Build 932:	0.0%
Covered Lines:	130
Relevant Lines:	157

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 934

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 82.803%

---

Totals
Change from base Build 932:	0.0%
Covered Lines:	130
Relevant Lines:	157

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 934

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 82.803%

---

Totals
Change from base Build 932:	0.0%
Covered Lines:	130
Relevant Lines:	157

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 934

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 82.803%

---

Totals
Change from base Build 932:	0.0%
Covered Lines:	130
Relevant Lines:	157

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 934

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 82.803%

---

Totals
Change from base Build 932:	0.0%
Covered Lines:	130
Relevant Lines:	157

---

💛 - Coveralls

[fingolfin]

I have no idea what this does, but I trust that @vtjnash knows what he does (in this case, at least 😝 )