Ensure mapping values are quoted when they contain a : separtor

This change prevents issue when the encoded yaml is invalid:

This object:    { key = "value: value" }
Is encoded as:  key: value: value
Instead of:     key: "value: value"

src/Data/Aeson/Yaml.hs

@@ -139,7 +139,8 @@ encodeText canMultiline alwaysQuote level s
       s /= "" && -- s is not empty
       Text.all isAllowed s && -- s consists of acceptable chars
       (Data.Char.isAlpha headS || -- head of s is a char in A-Z or a-z or indicates a filepath
-       headS == '/')
+       headS == '/') &&
+       not (Text.isInfixOf ": " s) -- s contains a mapping separator
     isBoolString
       | Text.length s > 5 = False
       | otherwise =

test/Test/Data/Aeson/Yaml.hs

@@ -215,7 +215,7 @@ tcHelloWorld =
     { tcName = "Hello World"
     , tcInput =
         [s|
-{ "image": "node 10.15.3"
+{ "image": "node: 10.15.3"
 , "pipelines":
   { "default":
     [ { "step":
@@ -230,7 +230,7 @@ tcHelloWorld =
 }
 |]
     , tcOutput =
-        [s|image: node 10.15.3
+        [s|image: "node: 10.15.3"
 pipelines:
   default:
     - step: