Fix absolute path resolution from remote module

[kt3k]

This PR fixes the absolute path resolution from the remote module.

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closes #203

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With this change, jspm seems working:

$ cat test.ts 
import React from "https://dev.jspm.io/react";
console.log(React);
$ ./target/debug/deno --reload test.ts 
Compiling file:///Users/kt3k/s/deno/test.ts
Downloading https://dev.jspm.io/react
Downloading https://dev.jspm.io/npm:[email protected]/index.dew.js
Downloading https://dev.jspm.io/npm:[email protected]/cjs/react.development.dew.js
Downloading https://dev.jspm.io/npm:object-assign@4?dew
Downloading https://dev.jspm.io/npm:prop-types@15/checkPropTypes?dew
Downloading https://dev.jspm.io/npm:[email protected]/cjs/react.development.dew.js
Downloading https://dev.jspm.io/npm:object-assign@4?dew
Downloading https://dev.jspm.io/npm:prop-types@15/checkPropTypes?dew
Downloading https://dev.jspm.io/npm:[email protected]/index.dew.js
Downloading https://dev.jspm.io/npm:[email protected]/checkPropTypes.dew.js
Downloading https://dev.jspm.io/npm:[email protected]/lib/ReactPropTypesSecret.dew.js
Downloading https://dev.jspm.io/npm:[email protected]/lib/ReactPropTypesSecret.dew.js
Downloading https://dev.jspm.io/react
Downloading https://dev.jspm.io/npm:[email protected]/index.dew.js
Downloading https://dev.jspm.io/npm:[email protected]/cjs/react.development.dew.js
Downloading https://dev.jspm.io/npm:object-assign@4?dew
Downloading https://dev.jspm.io/npm:[email protected]/index.dew.js
Downloading https://dev.jspm.io/npm:prop-types@15/checkPropTypes?dew
Downloading https://dev.jspm.io/npm:[email protected]/checkPropTypes.dew.js
Downloading https://dev.jspm.io/npm:[email protected]/lib/ReactPropTypesSecret.dew.js
{ Children, createRef, Component, PureComponent, createContext, forwardRef, lazy, memo, useCallback, useContext, useEffect, useImperativeHandle, useDebugValue, useLayoutEffect, useMemo, useReducer, useRef, useState, Fragment, StrictMode, Suspense, createElement, cloneElement, createFactory, isValidElement, version, unstable_ConcurrentMode, unstable_Profiler, __SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED }

[ry]

LGTM