Correct the url that is used when adding a label to an issue

src/main/java/io/spring/issuebot/github/GitHubTemplate.java

@@ -130,7 +130,8 @@ public class GitHubTemplate implements GitHubOperations {
 		Map<String, Object> body = new HashMap<>();
 		body.put("labels", Arrays.asList(labelName));
 		ResponseEntity<Label[]> response = this.rest.exchange(
-				new RequestEntity<>(body, HttpMethod.POST, URI.create(issue.getUrl())),
+				new RequestEntity<>(body, HttpMethod.POST,
+						URI.create(issue.getLabelsUrl().replace("{/name}", ""))),
 				Label[].class);
 		if (response.getStatusCode() != HttpStatus.OK) {
 			log.warn("Failed to add label to issue. Response status: "

src/test/java/io/spring/issuebot/github/GitHubTemplateTests.java

@@ -158,11 +158,12 @@ public class GitHubTemplateTests {
 
 	@Test
 	public void addLabelToIssue() {
-		this.server.expect(requestTo("issueUrl")).andExpect(method(HttpMethod.POST))
+		this.server.expect(requestTo("labelsUrl")).andExpect(method(HttpMethod.POST))
 				.andExpect(basicAuth())
 				.andExpect(content().string("{\"labels\":[\"test\"]}")).andRespond(
 						withSuccess("[{\"name\":\"test\"}]", MediaType.APPLICATION_JSON));
-		Issue issue = new Issue("issueUrl", null, null, null, null, null, null, null);
+		Issue issue = new Issue("issueUrl", null, null, "labelsUrl{/name}", null, null,
+				null, null);
 		Issue modifiedIssue = this.gitHub.addLabel(issue, "test");
 		assertThat(modifiedIssue.getLabels(), hasSize(1));
 	}