Try loading formatter by relative dir then by name

This commit makes it possible to load a custom formatter that is
not relative to the current working directory, such as one installed
globally, or via Yarn PNP.

src/formatter/builder.ts

@@ -103,8 +103,15 @@ const FormatterBuilder = {
   },
 
   loadCustomFormatter(customFormatterPath: string, cwd: string) {
-    const fullCustomFormatterPath = path.resolve(cwd, customFormatterPath)
-    const CustomFormatter = require(fullCustomFormatterPath) // eslint-disable-line @typescript-eslint/no-var-requires
+    let CustomFormatter = null
+
+    try {
+      const fullCustomFormatterPath = path.resolve(cwd, customFormatterPath)
+      CustomFormatter = require(fullCustomFormatterPath) // eslint-disable-line @typescript-eslint/no-var-requires
+    } catch {
+      CustomFormatter = require(customFormatterPath) // eslint-disable-line @typescript-eslint/no-var-requires
+    }
+
     if (typeof CustomFormatter === 'function') {
       return CustomFormatter
     } else if (