extension/src/goEnvironmentStatus: fix error string

Should've used `` to enable variable substitution

For #3386

Change-Id: I94bc823b0c959637f6d8b5a22fa90a2a76ba84d8
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/586255
Commit-Queue: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>
kokoro-CI: kokoro <noreply+kokoro@google.com>

extension/src/goEnvironmentStatus.ts

@@ -227,7 +227,7 @@ async function downloadGo(goOption: GoEnvironmentOption): Promise<GoEnvironmentO
 			});
 			if (result) {
 				outputChannel.error(`Error installing ${goOption.binpath}: ${result}`);
-				throw new Error('Could not install ${goOption.binpath}');
+				throw new Error(`Could not install ${goOption.binpath} - check logs in the "Go" output channel`);
 			}
 			// run `goX.X download`
 			const goXExecutable = getBinPath(newExecutableName);