OpenAPIImporter.java detection of yaml vs json is flawed
Using this logic:
```
        while ((line = reader.readLine()) != null) {
            line = line.trim();
            // Check is we start with json object or array definition.
            if (line.startsWith("{") || line.startsWith("[")) {
               isYaml = false;
               break;
            }
            if (line.startsWith("---")) {
               isYaml = true;
               break;
            }
         }
```
To detect the file format is prone to fail. My import job started failing this morning for my api.yaml file when a new revision was commited, as it looks like this now:
```
openapi: 3.0.2
info:
    title: Five
paths:
    /api/notifications:
        summary: Notifications
        description: Return a user list notifications
        get:
            summary: Returns a list of notifications
            responses:
                '200':
                    description: List of notifications
                    content:
                        application/json:
                            schema:
                                type: array
                                items:
                                    $ref: '#/components/schemas/Notification'
                            examples:
                                return one notification:
                                    value: |-
                                        [
                                            {
```

Those two lines starting with [ and { made microcks think I'm using a json file, and fail to execute the ObjectMapper.

What made this worse is that code on line 93 is swallowing the real exception, so I had to debug the code to figure out the root cause:
```
      } catch (Exception e) {
         throw new IOException("OpenAPI spec file");
      }
```
diff --git a/src/main/java/io/github/microcks/util/openapi/OpenAPIImporter.java b/src/main/java/io/github/microcks/util/openapi/OpenAPIImporter.java
index b91e0667..af76a0e3 100644
--- a/src/main/java/io/github/microcks/util/openapi/OpenAPIImporter.java
+++ b/src/main/java/io/github/microcks/util/openapi/OpenAPIImporter.java
@@ -71,7 +71,7 @@ public class OpenAPIImporter implements MockRepositoryImporter {
                isYaml = false;
                break;
             }
-            else if (line.startsWith("---") || line.startsWith("openapi: 3")) {
+            else if (line.startsWith("---") || line.matches("(openapi: ["']?3.*))") {
                isYaml = true;
                break;
             }
diff --git a/src/test/resources/io/github/microcks/util/openapi/cars-openapi-with-json.yaml b/src/test/resources/io/github/microcks/util/openapi/cars-openapi-with-json.yaml
index baea1434..afe1feeb 100644
--- a/src/test/resources/io/github/microcks/util/openapi/cars-openapi-with-json.yaml
+++ b/src/test/resources/io/github/microcks/util/openapi/cars-openapi-with-json.yaml
@@ -85,4 +85,4 @@ components:
       value: laurent
 tags:
 - name: car
-  description:
\ No newline at end of file
+  description: Car Ownership
\ No newline at end of file
['src/main/java/io/github/microcks/util/openapi/OpenAPIImporter.java', 'src/test/resources/io/github/microcks/util/openapi/cars-openapi-with-json.yaml']