bump the version to 1.0.2 in the installation instructions

 Merged changes michaeljguarino fn `normalize/1`

Summary: Merged new function `normalize/1` and other refactoring thanks to the fork [fork](https://github.com/hellonarrativ/ex_gtin)
 and @michaeljguarino

Details:

- Merged [7a1a0fc(hellonarrativ@7a1a0fc) from [fork](https://github.com/hellonarrativ/ex_gtin) - @cdesch
- Adding `normalize/1` and tests to convert a GTIN or ISBN to GTIN-14 format - Big Thanks to @michaeljguarino!
- Update `gtin_check_digit`, `generate_gtin_code` to use capture operators `&` - Big Thanks to @michaeljguarino!
- Add `()` to `generate_check_digit` functions - Big Thanks to @michaeljguarino!
- Fix Formatting of `multiply_and_sum_array`, `subtract_from_nearest_multiple_of_ten`, `mult_by_index_code` and `find_gs1_prefix_country` - Big Thanks to @michaeljguarino!
- Added tests for GTIN-8, GTIN-12, GTIN 14 - @cdesch

Release of 1.0.0

- *BREAKING CHANGE* `generate/1` - Formerly would return the result. It now returns the result in an atom e.g. `{:ok, "6291041500213"}`  - @cdesch
- Added `generate!/1` - Raises `ArgumentError` if invalid  - @cdesch
- Added `validate!/1`- Raises `ArgumentError` if invalid  - @cdesch
- Deprecated `generate_gtin` for `generate`. `generate_gtin` will be removed in version `1.0.1` - @cdesch
- Deprecated `check_gtin` for `validate`. `check_gtin` will be removed in version `1.0.1` - @cdesch
- Updated README with changes
- Fixed README markdown issues for code indentation

Changing function names to generate and validate

- Deprecated `generate_gtin` for `generate`. `generate_gtin` will be removed in version `0.5.0`
- Deprecated `check_gtin` for `validated`. `check_gtin` will be removed in version `0.5.0`
- Validated Functionality with Elixir 1.9.1 and Elixir 1.7.4
- README Updates with additional information
- Credo Fixes
- Updating Credo from `0.10.0` to `1.1.2` - @cdesch
- Updating Coveralls from `0.9.2` to `0.11.1` - @cdesch
- Updating ExDocs from `0.19.1` to `0.21.1` - @cdesch

- Adding `describe` groupings to tests - @cdesch

Validating Elixir 1.7.2 and updating libs

- Reformatted CHANGELOG.md - @cdesch
- Testing with Elixir 1.7.2 - @cdesch
- Added UPC acronym definition to README.md - @cdesch
- Updating Credo from `0.9.2` to `0.10.0` - @cdesch
- Updating Coveralls from `0.8.2` to `0.9.2` - @cdesch

Updated dependencies and fixed Credo Errors

Added GS1 Prefix Look up `gs1_prefix_country`

Signed-off-by: Chris Desch <cdesch@gmail.com>

Bumping the version

Signed-off-by: Chris Desch <cdesch@gmail.com>

Updating credo,exdoc and coveralls

Signed-off-by: Chris Desch <cdesch@gmail.com>