Add stripHexPrefix

[spacesailor24]

Description

Adds missing stripHexPrefix method

Fixes #3776

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:unit with success.
• I ran npm run test:cov and my test cases cover all the lines and branches of the added code.
• I ran npm run build and tested dist/web3.min.js in a browser.
• I have tested my code on the live network.
• I have checked the Deploy Preview and it looks correct.
• I have updated the CHANGELOG.md file in the root folder.

[coveralls]

Coverage increased (+2.4%) to 80.413% when pulling ac38da1 on wyatt/3776-stripHexPrefix into edf481d on 1.x.

[frankiebee]

dont bump the versions in this pr please. also if their are no new packages dont commit the package*.json files

[frankiebee]

oh my gosh! you are so good at writing tests!

[GregTheGreek]

can you add a test like:

value: "0xfffff0x0fffffffffff0xffffff0x"
expected: "fffff0x0fffffffffff0xffffff0x"

to ensure we're preserving the 0x(s) that may appear in the middle (even though this breaks convention of hex, better safe than sorry)

[spacesailor24]

In this case, the original value (0xfffff0x0fffffffffff0xffffff0x) would be returned since it fails the isHex check:

var isHex = function (hex) {
    return ((_.isString(hex) || _.isNumber(hex)) && /^(-0x|0x)?[0-9a-f]*$/i.test(hex));
};

[spacesailor24]

oh my gosh! you are so good at writing tests!

Wish I could take credit for the setup, but it was basically all copy/paste