Fix incorrect hyphens in the top level readme (#545)

Some hyphens got replaced by special character hyphens, which cause errors when copied into a command line. Replace with the correct version.

Author: a-maurice

README.md

@@ -81,7 +81,7 @@ Expected output artifact is
 ### Building for certain library
 
 ``` bash
-python scripts/build_scripts/build_zips.py —-platform=<target platform> --targets=<lib1> -–targets=<lib2>
+python scripts/build_scripts/build_zips.py --platform=<target platform> --targets=<lib1> --targets=<lib2>
 ```
 
 > **Note:** Supported library names: analytics, auth, crashlytics, database, dynamic_links, firestore, functions, installations, messaging, remote_config, storage
@@ -103,23 +103,23 @@ Copy the zip file for each platforms to one folder, referred to as assets_zip_di
 And then run:
 
 ``` bash
-python scripts/build_scripts/build_package.py --zip_dir=<assets_zip_dir> –output=<output dir>
+python scripts/build_scripts/build_package.py --zip_dir=<assets_zip_dir> --output=<output dir>
 ```
 
 ### Packaging tgz
 
 With the same assets_zip_dir, we can run:
 
 ``` bash
-python scripts/build_scripts/build_package.py --zip_dir=<assets_zip_dir> –output=<output dir> --output_upm=True
+python scripts/build_scripts/build_package.py --zip_dir=<assets_zip_dir> --output=<output dir> --output_upm=True
 ```
 
 ### Packing for certain library
 
 If we build only certain subset of the libraries like in [Building for certain library](#building-for-certain-library), we can copy the built artifacts into assets_zip_dir, and then run:
 
 ``` bash
-python scripts/build_scripts/build_package.py --zip_dir=<assets_zip_dir> -–output=<output dir> --apis=<lib1,lib2>
+python scripts/build_scripts/build_package.py --zip_dir=<assets_zip_dir> --output=<output dir> --apis=<lib1,lib2>
 ```
 
 ## Including in Project
@@ -139,4 +139,4 @@ The contents of this repository is licensed under the
 [Apache License, version 2.0](http://www.apache.org/licenses/LICENSE-2.0).
 
 Your use of Firebase is governed by the
-[Terms of Service for Firebase Services](https://firebase.google.com/terms/).
+[Terms of Service for Firebase Services](https://firebase.google.com/terms/).