Merge pull request #103 from square/cs/no-print

Return error instead of printing to stderr in lib

.travis.yml

@@ -10,7 +10,7 @@ go:
 
 before_install:
   - go get github.com/Masterminds/glide
-  - pip install cram --user `whoami`
+  - pip install cram --user
 
 install:
   - go build .

lib/certs.go

@@ -196,7 +196,7 @@ func readCertsFromStream(reader io.Reader, filename string, format string, passw
 		}
 		blocks, err := pkcs12.ToPEM(data, password(""))
 		if err != nil || len(blocks) == 0 {
-			fmt.Fprint(os.Stderr, "keystore appears to be empty or password was incorrect\n")
+			return fmt.Errorf("keystore appears to be empty or password was incorrect\n")
 		}
 		for _, block := range blocks {
 			block.Headers = mergeHeaders(block.Headers, headers)