Fix the failing tests, include Go 1.13 in test matrix

.travis.yml

@@ -4,6 +4,7 @@ go:
   - 1.10.x
   - 1.11.x
   - 1.12.x
+  - 1.13.x
   - tip
 
 matrix:

src/util.ts

@@ -940,7 +940,20 @@ export function runGodoc(cwd: string, packagePath: string, receiver: string, sym
 				if (err) {
 					return reject(err.message || stderr);
 				}
+				let doc = '';
 				const godocLines = stdout.split('\n');
+				if (!godocLines.length) {
+					return resolve(doc);
+				}
+
+				// Recent versions of Go have started to include the package statement
+				// tht we dont need.
+				if (godocLines[0].startsWith('package ')) {
+					godocLines.splice(0, 1);
+					if (!godocLines[0].trim()) {
+						godocLines.splice(0, 1);
+					}
+				}
 
 				// Skip trailing empty lines
 				let lastLine = godocLines.length - 1;
@@ -950,7 +963,6 @@ export function runGodoc(cwd: string, packagePath: string, receiver: string, sym
 					}
 				}
 
-				let doc = '';
 				for (let i = 1; i <= lastLine; i++) {
 					if (godocLines[i].startsWith('    ')) {
 						doc += godocLines[i].substring(4) + '\n';

test/fixtures/gogetdocTestData/test.go

@@ -26,7 +26,7 @@ func main() {
 
 // Hello is a method on the struct ABC. Will signature help understand this correctly
 func (abcd *ABC) Hello(s string, exclaim bool) string {
-	net.CIDRMask(10, 20)
+	net.IPv4Mask(0, 0, 0, 0)
 	if exclaim {
 		s = s + "!"
 	}

test/integration/extension.test.ts

@@ -248,7 +248,7 @@ It returns the number of bytes written and any write error encountered.
 			[new vscode.Position(40, 23), 'package math', 'Package math provides basic constants and mathematical functions.\n\nThis package does not guarantee bit-identical results across architectures.\n'],
 			[new vscode.Position(19, 6), 'func Println(a ...interface{}) (n int, err error)', printlnDoc],
 			[new vscode.Position(27, 14), 'type ABC struct {\n    a int\n    b int\n    c int\n}', 'ABC is a struct, you coudn\'t use Goto Definition or Hover info on this before\nNow you can due to gogetdoc and go doc\n'],
-			[new vscode.Position(28, 6), 'func CIDRMask(ones, bits int) IPMask', 'CIDRMask returns an IPMask consisting of `ones\' 1 bits\nfollowed by 0s up to a total length of `bits\' bits.\nFor a mask of this form, CIDRMask is the inverse of IPMask.Size.\n']
+			[new vscode.Position(28, 6), 'func IPv4Mask(a, b, c, d byte) IPMask', 'IPv4Mask returns the IP mask (in 4-byte form) of the\nIPv4 mask a.b.c.d.\n']
 		];
 		const config = Object.create(vscode.workspace.getConfiguration('go'), {
 			'docsTool': { value: 'gogetdoc' }