fix the error info of 'sourceType' (babel#572)

Author: blackmiaool

src/parser/statement.js

@@ -105,7 +105,7 @@ pp.parseStatement = function (declaration, topLevel) {
         }
 
         if (!this.inModule) {
-          this.raise(this.state.start, "'import' and 'export' may appear only with 'sourceType: module'");
+          this.raise(this.state.start, "'import' and 'export' may appear only with 'sourceType: \"module\"'");
         }
       }
       return starttype === tt._import ? this.parseImport(node) : this.parseExport(node);

test/fixtures/esprima/es2015-identifier/invalid_expression_await/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "'import' and 'export' may appear only with 'sourceType: module' (1:0)"
+  "throws": "'import' and 'export' may appear only with 'sourceType: \"module\"' (1:0)"
 }

test/fixtures/esprima/es2015-identifier/invalid_var_await/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "'import' and 'export' may appear only with 'sourceType: module' (1:0)"
+  "throws": "'import' and 'export' may appear only with 'sourceType: \"module\"' (1:0)"
 }

test/fixtures/esprima/es2015-yield/invalid-yield-generator-export-default/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "'import' and 'export' may appear only with 'sourceType: module' (1:0)"
+  "throws": "'import' and 'export' may appear only with 'sourceType: \"module\"' (1:0)"
 }